diff --git a/apps/machine/.env.example b/apps/machine/.env.example
index ec66f81..8748c21 100644
--- a/apps/machine/.env.example
+++ b/apps/machine/.env.example
@@ -93,3 +93,29 @@ VITE_SPIRE_SEED=
 # Set to 'true' for development/demo environments only
 # When false (production default), initialization failures show a maintenance screen
 # VITE_ALLOW_MOCK_FALLBACK=true
+
+# =============================================================================
+# Access Control (ADR-003)
+# =============================================================================
+
+# Badge-to-enter gate. When disabled (default), the machine boots straight to
+# idle exactly as before. When enabled, it boots into a locked screen and
+# requires a credential (prototype: an npub QR scanned by the camera, with an
+# optional PIN) before transactions are reachable.
+# ACCESS_CONTROL_ENABLED=true
+
+# Prototype posture: admit ANY valid npub when the allow-list has no match.
+# Turn OFF once a real allow-list (/var/lib/bitspire/access.json) is provisioned.
+# ACCESS_OPEN_ENROLLMENT=true
+
+# Allow the on-screen runtime dev/operator unlock button (default: allowed when
+# the gate is on). Set to 'false' to hide it on a locked-down deployment.
+# ACCESS_DEV_UNLOCK=false
+
+# Per-machine salt for hashing credentials/PINs. Provision a real value in
+# production (or in access.json); a fixed default is used if unset.
+# ACCESS_SALT=change-me-per-machine
+
+# Build/dev bypass — forces the gate OPEN even when enabled (browser dev / CI).
+# Renderer-side (Vite) flag, never set in a production image.
+# VITE_SKIP_ACCESS_GATE=true
diff --git a/apps/machine/electron/main.ts b/apps/machine/electron/main.ts
index 6cfcb20..736d89d 100644
--- a/apps/machine/electron/main.ts
+++ b/apps/machine/electron/main.ts
@@ -164,6 +164,61 @@ function loadBranding(): BrandingConfig | null {
   return { title, theme, customColors, customColorsDark, logoDataUrl, logoDarkDataUrl }
 }
 
+// Access-control config loader (ADR-003). Env toggles the gate; an optional
+// /var/lib/bitspire/access.json carries the salt + allow-list. Defaults OFF —
+// a machine with neither env nor file behaves as if there is no access layer.
+// The allow-list shape mirrors the renderer's AllowListEntry (authorize.ts);
+// duplicated here to avoid a cross-project (electron↔renderer) import.
+interface AccessAllowListEntry {
+  idHash: string
+  role: 'user' | 'operator'
+  pinHash?: string
+  label?: string
+}
+function loadAccessControl() {
+  // Env provides defaults; access.json (writable, operator-provisioned — same
+  // spirit as branding/) overrides them, so the gate can be toggled on a
+  // deployed machine by dropping a file + restarting the service, with no image
+  // rebuild. Defaults OFF.
+  let enabled = process.env.ACCESS_CONTROL_ENABLED === 'true'
+  // Dev unlock allowed by default when the gate is on; opt out explicitly.
+  let devUnlock = process.env.ACCESS_DEV_UNLOCK !== 'false'
+  let openEnrollment = process.env.ACCESS_OPEN_ENROLLMENT === 'true'
+  let salt = process.env.ACCESS_SALT || ''
+  let allowList: AccessAllowListEntry[] = []
+
+  const jsonPath = path.join(
+    fs.existsSync('/var/lib/bitspire') ? '/var/lib/bitspire' : process.cwd(),
+    'access.json'
+  )
+  if (fs.existsSync(jsonPath)) {
+    try {
+      const raw = JSON.parse(fs.readFileSync(jsonPath, 'utf-8'))
+      if (typeof raw.enabled === 'boolean') enabled = raw.enabled
+      if (typeof raw.devUnlock === 'boolean') devUnlock = raw.devUnlock
+      if (typeof raw.openEnrollment === 'boolean') openEnrollment = raw.openEnrollment
+      if (typeof raw.salt === 'string' && raw.salt) salt = raw.salt
+      if (Array.isArray(raw.allowList)) {
+        allowList = (raw.allowList as unknown[]).filter(
+          (e): e is AccessAllowListEntry =>
+            !!e &&
+            typeof (e as AccessAllowListEntry).idHash === 'string' &&
+            ((e as AccessAllowListEntry).role === 'user' ||
+              (e as AccessAllowListEntry).role === 'operator')
+        )
+      }
+    } catch (e) {
+      console.warn('[Electron] Failed to parse access.json:', e)
+    }
+  }
+
+  // A gated machine needs a stable salt for deterministic hashing. Fall back to
+  // a fixed default (prototype); production should provision a real salt.
+  if (!salt) salt = 'bitspire-access-v1'
+
+  return { enabled, devUnlock, openEnrollment, salt, allowList }
+}
+
 // Determine if we're in development
 const isDev =
   process.env.ELECTRON_FORCE_PROD !== '1' &&
@@ -311,6 +366,9 @@ ipcMain.handle('get-config', () => {
 
     // Operator branding (logo/title/theme) — null when no override
     branding: loadBranding(),
+
+    // Access-control gate (ADR-003) — `enabled` defaults false (no gate).
+    accessControl: loadAccessControl(),
   }
 })
 
diff --git a/apps/machine/src/App.vue b/apps/machine/src/App.vue
index d9bce92..742c868 100644
--- a/apps/machine/src/App.vue
+++ b/apps/machine/src/App.vue
@@ -7,8 +7,9 @@ import { setBranding } from '@/composables/useBranding'
 import { classifyInitError } from '@/services/init-error'
 import { Badge } from '@/components/ui/badge'
 import { Button } from '@/components/ui/button'
-import { Sun, Moon } from 'lucide-vue-next'
 import PairingWizard from '@/components/PairingWizard.vue'
+import LockedView from '@/views/LockedView.vue'
+import ColorModeToggle from '@/components/ColorModeToggle.vue'
 
 const atmStore = useAtmStore()
 const route = useRoute()
@@ -289,6 +290,11 @@ function toggleLiveServices() {
       </Button>
     </div>
 
+    <!-- Access gate (ADR-003): shown when the machine is healthy but locked,
+         below the init/maintenance gates above. Never renders when access
+         control is disabled (the machine never dwells in `locked`). -->
+    <LockedView v-else-if="atmStore.isLocked" />
+
     <template v-else>
       <router-view />
 
@@ -340,16 +346,10 @@ function toggleLiveServices() {
       </div>
 
       <!-- Light/dark toggle (production only — debug panel has this in dev) -->
-      <Button
+      <ColorModeToggle
         v-if="!atmStore.allowMockFallback"
-        variant="outline"
-        class="fixed bottom-3 right-3 lg:bottom-6 lg:right-6 z-50 h-10 px-3 py-1 text-sm rounded-lg lg:h-[7vh] lg:min-h-[70px] lg:px-8 lg:py-3 lg:text-2xl lg:rounded-xl gap-2 lg:gap-3"
-        @click="colorMode = colorMode === 'dark' ? 'light' : 'dark'"
-      >
-        <Sun v-if="colorMode === 'dark'" class="w-5 h-5 lg:w-7 lg:h-7" />
-        <Moon v-else class="w-5 h-5 lg:w-7 lg:h-7" />
-        {{ colorMode === 'dark' ? 'Light' : 'Dark' }}
-      </Button>
+        class="fixed bottom-3 right-3 z-50 lg:bottom-6 lg:right-6"
+      />
 
       <!-- Debug overlay (dev only) -->
       <div
diff --git a/apps/machine/src/components/ColorModeToggle.vue b/apps/machine/src/components/ColorModeToggle.vue
new file mode 100644
index 0000000..0578adc
--- /dev/null
+++ b/apps/machine/src/components/ColorModeToggle.vue
@@ -0,0 +1,33 @@
+<script setup lang="ts">
+/**
+ * Light/dark toggle — the single reusable control for switching color mode.
+ *
+ * Kiosk-sized by default (large touch target for a public display). colorMode
+ * is global + persisted (toggles `.dark` on <html>, and dark mode pulls
+ * branding.json's dark palette + logo-dark.png), so this stays in sync
+ * wherever it's used. Position it via a fallthrough `class` on the consumer,
+ * e.g. `<ColorModeToggle class="fixed bottom-6 right-6" />`.
+ */
+import { useTheme } from '@/composables/useTheme'
+import { Button } from '@/components/ui/button'
+import { Sun, Moon } from 'lucide-vue-next'
+
+const { colorMode } = useTheme()
+
+function toggle() {
+  colorMode.value = colorMode.value === 'dark' ? 'light' : 'dark'
+}
+</script>
+
+<template>
+  <Button
+    variant="outline"
+    class="h-10 gap-2 rounded-lg px-3 py-1 text-sm lg:h-[7vh] lg:min-h-[70px] lg:gap-3 lg:rounded-xl lg:px-8 lg:py-3 lg:text-2xl"
+    :aria-label="colorMode === 'dark' ? 'Switch to light mode' : 'Switch to dark mode'"
+    @click="toggle"
+  >
+    <Sun v-if="colorMode === 'dark'" class="h-5 w-5 lg:h-7 lg:w-7" />
+    <Moon v-else class="h-5 w-5 lg:h-7 lg:w-7" />
+    {{ colorMode === 'dark' ? 'Light' : 'Dark' }}
+  </Button>
+</template>
diff --git a/apps/machine/src/services/access/__tests__/authorize.test.ts b/apps/machine/src/services/access/__tests__/authorize.test.ts
new file mode 100644
index 0000000..0f175af
--- /dev/null
+++ b/apps/machine/src/services/access/__tests__/authorize.test.ts
@@ -0,0 +1,113 @@
+import { describe, it, expect } from 'vitest'
+import { npubEncode, nprofileEncode } from 'nostr-tools/nip19'
+import { authorize, hashId, hashPin, type AllowListEntry } from '../authorize'
+
+const SALT = 'test-salt'
+const HEX_A = 'aa'.repeat(32)
+const HEX_B = 'bb'.repeat(32)
+const NPUB_A = npubEncode(HEX_A)
+const NPUB_B = npubEncode(HEX_B)
+
+describe('access authorize (ADR-003)', () => {
+  describe('open enrollment (prototype)', () => {
+    it('grants any valid npub as user', async () => {
+      const out = await authorize({ kind: 'npub', npub: NPUB_A }, [], {
+        salt: SALT,
+        openEnrollment: true,
+      })
+      expect(out.status).toBe('granted')
+      expect(out).toMatchObject({ status: 'granted', role: 'user' })
+    })
+
+    it('rejects a stray / non-npub QR', async () => {
+      const out = await authorize({ kind: 'npub', npub: 'https://example.com/not-an-npub' }, [], {
+        salt: SALT,
+        openEnrollment: true,
+      })
+      expect(out.status).toBe('denied')
+      expect(out).toMatchObject({ reason: 'not a valid npub' })
+    })
+
+    it('accepts a `nostr:` URI prefix (with surrounding whitespace)', async () => {
+      const out = await authorize({ kind: 'npub', npub: `  nostr:${NPUB_A}\n` }, [], {
+        salt: SALT,
+        openEnrollment: true,
+      })
+      expect(out.status).toBe('granted')
+    })
+
+    it('accepts an nprofile and resolves to the same identity as its npub', async () => {
+      const nprofile = nprofileEncode({ pubkey: HEX_A, relays: ['wss://relay.example'] })
+      const viaNprofile = await authorize({ kind: 'npub', npub: nprofile }, [], {
+        salt: SALT,
+        openEnrollment: true,
+      })
+      const viaNpub = await authorize({ kind: 'npub', npub: NPUB_A }, [], {
+        salt: SALT,
+        openEnrollment: true,
+      })
+      expect(viaNprofile.status).toBe('granted')
+      // Same underlying pubkey → same credential hash.
+      expect(viaNprofile.credentialIdHash).toBe(viaNpub.credentialIdHash)
+    })
+  })
+
+  describe('allow-list (closed)', () => {
+    it('denies an unlisted npub when not open-enrollment', async () => {
+      const out = await authorize({ kind: 'npub', npub: NPUB_A }, [], { salt: SALT })
+      expect(out).toMatchObject({ status: 'denied', reason: 'not authorized' })
+    })
+
+    it('grants a listed npub with its role, no PIN', async () => {
+      const entry: AllowListEntry = { idHash: await hashId(HEX_A, SALT), role: 'operator' }
+      const out = await authorize({ kind: 'npub', npub: NPUB_A }, [entry], { salt: SALT })
+      expect(out).toMatchObject({ status: 'granted', role: 'operator' })
+    })
+
+    it('does not match npub B against npub A entry', async () => {
+      const entry: AllowListEntry = { idHash: await hashId(HEX_A, SALT), role: 'user' }
+      const out = await authorize({ kind: 'npub', npub: NPUB_B }, [entry], { salt: SALT })
+      expect(out.status).toBe('denied')
+    })
+  })
+
+  describe('PIN second factor', () => {
+    const makeEntry = async (): Promise<AllowListEntry> => ({
+      idHash: await hashId(HEX_A, SALT),
+      role: 'user',
+      pinHash: await hashPin('1234', SALT),
+    })
+
+    it('asks for a PIN when one is configured and none supplied', async () => {
+      const out = await authorize({ kind: 'npub', npub: NPUB_A }, [await makeEntry()], { salt: SALT })
+      expect(out.status).toBe('pin-required')
+    })
+
+    it('grants on correct PIN', async () => {
+      const out = await authorize({ kind: 'npub', npub: NPUB_A }, [await makeEntry()], {
+        salt: SALT,
+        pin: '1234',
+      })
+      expect(out).toMatchObject({ status: 'granted', role: 'user' })
+    })
+
+    it('denies on wrong PIN', async () => {
+      const out = await authorize({ kind: 'npub', npub: NPUB_A }, [await makeEntry()], {
+        salt: SALT,
+        pin: '9999',
+      })
+      expect(out).toMatchObject({ status: 'denied', reason: 'incorrect PIN' })
+    })
+  })
+
+  describe('challenge credential (v2 seam)', () => {
+    it('is not yet authorized', async () => {
+      const out = await authorize(
+        { kind: 'challenge', pubkey: HEX_A, nonce: 'n', sig: 's' },
+        [],
+        { salt: SALT, openEnrollment: true }
+      )
+      expect(out.status).toBe('denied')
+    })
+  })
+})
diff --git a/apps/machine/src/services/access/authorize.ts b/apps/machine/src/services/access/authorize.ts
new file mode 100644
index 0000000..a6c99be
--- /dev/null
+++ b/apps/machine/src/services/access/authorize.ts
@@ -0,0 +1,141 @@
+/**
+ * Credential authorization (ADR-003).
+ *
+ * PROTOTYPE (this PR): a QR "badge" carrying an npub grants terminal access,
+ * with an OPTIONAL PIN as a second factor. Matching is against a local
+ * allow-list of hashed identities; `openEnrollment` admits any valid npub
+ * (no allow-list) for early prototyping. Only salted hashes are compared or
+ * stored — never the raw npub/UID (KYC-free).
+ *
+ * Identity id per scan kind:
+ *   - npub      → hex pubkey (decoded, canonical), then hashed
+ *   - uid       → raw UID hashed (NFC, PR4)
+ *   - challenge → v2 seam (PR5), not yet authorized
+ */
+
+import { decode as nip19Decode } from 'nostr-tools/nip19'
+import type { AccessRole } from '@bitSpire/state-machine'
+import type { AccessScan } from './types'
+
+/** One authorized identity. `idHash` = hashId(<canonical id>, salt). */
+export interface AllowListEntry {
+  idHash: string
+  role: AccessRole
+  /** When set, access requires this PIN (hashPin(pin, salt)) as a 2nd factor. */
+  pinHash?: string
+  /** Optional operator-facing label (never a person's real identity). */
+  label?: string
+}
+
+export interface AuthorizeOptions {
+  /** Per-machine salt for all hashing. */
+  salt: string
+  /** Admit any valid credential when the allow-list has no match (prototype). */
+  openEnrollment?: boolean
+  /** PIN supplied on the follow-up call after a `pin-required` outcome. */
+  pin?: string
+}
+
+/**
+ * Three outcomes, so the caller can drive a two-step flow:
+ *  - `granted`      → send ACCESS_GRANTED
+ *  - `pin-required` → prompt for a PIN, then call authorize() again with `pin`
+ *  - `denied`       → send ACCESS_DENIED(reason)
+ */
+export type AuthorizeOutcome =
+  | { status: 'granted'; role: AccessRole; credentialIdHash: string }
+  | { status: 'pin-required'; credentialIdHash: string }
+  | { status: 'denied'; credentialIdHash: string; reason: string }
+
+/** Salted SHA-256, hex-encoded. */
+async function sha256Hex(input: string): Promise<string> {
+  const data = new TextEncoder().encode(input)
+  const digest = await crypto.subtle.digest('SHA-256', data)
+  return [...new Uint8Array(digest)].map((b) => b.toString(16).padStart(2, '0')).join('')
+}
+
+export const hashId = (id: string, salt: string): Promise<string> => sha256Hex(`id:${salt}:${id}`)
+export const hashPin = (pin: string, salt: string): Promise<string> => sha256Hex(`pin:${salt}:${pin}`)
+
+/**
+ * Resolve a scan to a canonical identity string, or `null` if malformed.
+ * npub is decoded to its hex pubkey so npub/hex forms compare equal and a
+ * stray (non-npub) QR is rejected.
+ */
+function canonicalId(scan: AccessScan): string | null {
+  if (scan.kind === 'uid') return scan.uid || null
+  if (scan.kind === 'challenge') return null // v2 — handled separately
+  // Tolerate real-world nostr QR shapes: a bare `npub1…`, a `nostr:` URI
+  // prefix, and `nprofile1…` (npub + relay hints, what many clients export).
+  const raw = scan.npub.trim().replace(/^nostr:/i, '')
+  try {
+    const decoded = nip19Decode(raw)
+    if (decoded.type === 'npub' && typeof decoded.data === 'string') {
+      return decoded.data
+    }
+    if (
+      decoded.type === 'nprofile' &&
+      decoded.data &&
+      typeof (decoded.data as { pubkey?: unknown }).pubkey === 'string'
+    ) {
+      return (decoded.data as { pubkey: string }).pubkey
+    }
+    return null
+  } catch {
+    return null
+  }
+}
+
+/**
+ * Decide whether a scanned credential is authorized.
+ * Always resolves (never throws) so the caller can uniformly react.
+ */
+export async function authorize(
+  scan: AccessScan,
+  allowList: AllowListEntry[],
+  opts: AuthorizeOptions
+): Promise<AuthorizeOutcome> {
+  if (scan.kind === 'challenge') {
+    return {
+      status: 'denied',
+      credentialIdHash: '',
+      reason: 'challenge-response credentials not yet supported',
+    }
+  }
+
+  const id = canonicalId(scan)
+  if (!id) {
+    return {
+      status: 'denied',
+      credentialIdHash: '',
+      reason: scan.kind === 'npub' ? 'not a valid npub' : 'invalid credential',
+    }
+  }
+
+  const credentialIdHash = await hashId(id, opts.salt)
+  const entry = allowList.find((e) => e.idHash === credentialIdHash)
+
+  if (!entry) {
+    if (opts.openEnrollment) {
+      return { status: 'granted', role: 'user', credentialIdHash }
+    }
+    return { status: 'denied', credentialIdHash, reason: 'not authorized' }
+  }
+
+  // No PIN configured → single-factor grant.
+  if (!entry.pinHash) {
+    return { status: 'granted', role: entry.role, credentialIdHash }
+  }
+
+  // PIN configured but not yet supplied → ask for it.
+  if (opts.pin === undefined) {
+    return { status: 'pin-required', credentialIdHash }
+  }
+
+  // PIN supplied → verify.
+  const pinHash = await hashPin(opts.pin, opts.salt)
+  if (pinHash !== entry.pinHash) {
+    return { status: 'denied', credentialIdHash, reason: 'incorrect PIN' }
+  }
+  return { status: 'granted', role: entry.role, credentialIdHash }
+}
diff --git a/apps/machine/src/services/access/index.ts b/apps/machine/src/services/access/index.ts
new file mode 100644
index 0000000..fb1e26c
--- /dev/null
+++ b/apps/machine/src/services/access/index.ts
@@ -0,0 +1,42 @@
+/**
+ * Access-control module surface (ADR-003).
+ *
+ * `availableAccessReaders()` returns the readers this device can run, in
+ * preference order: the camera npub-QR badge first (prototype, works on the
+ * batm3 today), the mock reader as a keyboard/console fallback. PR3 adds a
+ * Web-NFC reader and PR4 the serial `/dev/ttyNFC` reader ahead of these.
+ */
+
+import { QrNpubAccessReader } from './qr-npub-reader'
+import { MockAccessReader } from './mock-reader'
+import type { AccessReader } from './types'
+
+export type {
+  AccessReader,
+  AccessReaderKind,
+  AccessReaderStartOptions,
+  AccessScan,
+  AccessRole,
+  StopCapture,
+} from './types'
+export { QrNpubAccessReader } from './qr-npub-reader'
+export { MockAccessReader, MOCK_NPUB } from './mock-reader'
+export { authorize, hashId, hashPin } from './authorize'
+export type { AllowListEntry, AuthorizeOptions, AuthorizeOutcome } from './authorize'
+
+/** All readers in preference order, regardless of availability. */
+export function allAccessReaders(): AccessReader[] {
+  // PR3: WebNfcAccessReader, PR4: SerialNfcAccessReader — inserted ahead of the
+  // camera once real NFC hardware is present.
+  return [new QrNpubAccessReader(), new MockAccessReader()]
+}
+
+/**
+ * Only the readers this device can run, in preference order. The mock reader
+ * is always available, so it lands last as a guaranteed fallback.
+ */
+export async function availableAccessReaders(): Promise<AccessReader[]> {
+  const readers = allAccessReaders()
+  const flags = await Promise.all(readers.map((r) => r.isAvailable()))
+  return readers.filter((_, i) => flags[i])
+}
diff --git a/apps/machine/src/services/access/mock-reader.ts b/apps/machine/src/services/access/mock-reader.ts
new file mode 100644
index 0000000..c918b18
--- /dev/null
+++ b/apps/machine/src/services/access/mock-reader.ts
@@ -0,0 +1,53 @@
+/**
+ * Mock access reader (ADR-003) — SCAFFOLD, no hardware.
+ *
+ * A keyboard/console fallback for when no camera or NFC reader is present
+ * (headless dev, CI, a batm3 with a dead camera). Emits an npub scan on
+ * demand via two triggers:
+ *   - `window.__bitspireMockCard(npub?)` — from the LockedView dev button or
+ *     the devtools console.
+ *   - the `F9` key — a quick tap on the physical machine.
+ *
+ * Registered only when it is the sole available reader (see `index.ts`), so it
+ * never shadows the real camera/NFC path.
+ */
+
+import { npubEncode } from 'nostr-tools/nip19'
+import type { AccessReader, AccessReaderStartOptions, StopCapture } from './types'
+
+/**
+ * Default npub the mock emits when none is supplied — derived from a fixed
+ * (all-ones) hex pubkey so it carries a valid bech32 checksum and survives
+ * `authorize()`'s nip19 decode. Not a real key; dev-only.
+ */
+export const MOCK_NPUB = npubEncode('11'.repeat(32))
+
+interface MockCardGlobal {
+  __bitspireMockCard?: (npub?: string) => void
+}
+
+export class MockAccessReader implements AccessReader {
+  readonly kind = 'mock' as const
+  readonly label = 'Mock reader (dev)'
+
+  async isAvailable(): Promise<boolean> {
+    return true
+  }
+
+  async start(opts: AccessReaderStartOptions): Promise<StopCapture> {
+    const emit = (npub: string = MOCK_NPUB) => opts.onScan({ kind: 'npub', npub })
+
+    const g = globalThis as unknown as MockCardGlobal
+    g.__bitspireMockCard = emit
+
+    const onKey = (e: KeyboardEvent) => {
+      if (e.key === 'F9') emit()
+    }
+    window.addEventListener('keydown', onKey)
+
+    return () => {
+      window.removeEventListener('keydown', onKey)
+      if (g.__bitspireMockCard === emit) delete g.__bitspireMockCard
+    }
+  }
+}
diff --git a/apps/machine/src/services/access/qr-npub-reader.ts b/apps/machine/src/services/access/qr-npub-reader.ts
new file mode 100644
index 0000000..e95c507
--- /dev/null
+++ b/apps/machine/src/services/access/qr-npub-reader.ts
@@ -0,0 +1,79 @@
+/**
+ * QR-npub access reader (ADR-003, PROTOTYPE).
+ *
+ * Until the NFC reader hardware exists, the batm3's camera — the same one the
+ * pairing wizard uses — reads a QR "badge" that encodes the user's npub. The
+ * decoded npub is handed to `authorize()`, which admits it (optionally behind
+ * a PIN). This is a thin adapter onto the same `qr/dom.js` decode loop as
+ * `pairing/qr-source.ts`; see that file for the capture-resolution rationale.
+ *
+ * It emits the raw decoded string as an `npub` scan and lets `authorize()`
+ * validate it — a stray, non-npub QR is rejected there, not here.
+ */
+
+import { QRCanvas, frontalCamera, frameLoop } from 'qr/dom.js'
+import type { AccessReader, AccessReaderStartOptions, StopCapture } from './types'
+
+export class QrNpubAccessReader implements AccessReader {
+  readonly kind = 'qr-npub' as const
+  readonly label = 'Camera (npub QR)'
+
+  async isAvailable(): Promise<boolean> {
+    return (
+      typeof navigator !== 'undefined' &&
+      !!navigator.mediaDevices &&
+      typeof navigator.mediaDevices.getUserMedia === 'function'
+    )
+  }
+
+  async start(opts: AccessReaderStartOptions): Promise<StopCapture> {
+    const { onScan, onError, video } = opts
+    if (!video) throw new Error('QrNpubAccessReader requires a <video> element')
+
+    const camera = await frontalCamera(video)
+
+    // Match the pairing source's deliberate capture resolution (see
+    // pairing/qr-source.ts) — 1280x960 balances px/module against decode speed
+    // on this fixed-focus panel. Soft `ideal` so a camera that can't honor it
+    // degrades instead of throwing.
+    try {
+      const stream = video.srcObject
+      if (stream instanceof MediaStream) {
+        await stream.getVideoTracks()[0]?.applyConstraints({
+          width: { ideal: 1280 },
+          height: { ideal: 960 },
+        })
+      }
+    } catch (e) {
+      onError?.(e)
+    }
+
+    const canvas = new QRCanvas() // decode-only
+
+    let stopped = false
+    let cancel: (() => void) | null = null
+    const stop: StopCapture = () => {
+      if (stopped) return
+      stopped = true
+      cancel?.()
+      camera.stop()
+    }
+
+    cancel = frameLoop(() => {
+      if (stopped) return
+      try {
+        const result = camera.readFrame(canvas, true)
+        if (result) {
+          // Stop on first decode so one badge isn't ingested repeatedly; the
+          // store restarts the reader if authorization fails.
+          stop()
+          onScan({ kind: 'npub', npub: result.trim() })
+        }
+      } catch (e) {
+        onError?.(e)
+      }
+    })
+
+    return stop
+  }
+}
diff --git a/apps/machine/src/services/access/types.ts b/apps/machine/src/services/access/types.ts
new file mode 100644
index 0000000..b7719f7
--- /dev/null
+++ b/apps/machine/src/services/access/types.ts
@@ -0,0 +1,60 @@
+/**
+ * Access-control reader abstraction (ADR-003).
+ *
+ * Mirrors the `services/pairing` `PairingSource` seam: an `AccessReader`
+ * captures a credential from whatever hardware the machine has and hands an
+ * `AccessScan` to the store, which authorizes it and grants/denies terminal
+ * access. Implementations live next to this file:
+ *   - `qr-npub-reader.ts` — camera scans an npub QR "badge" (PROTOTYPE, works
+ *     on batm3 today — same camera the pairing wizard uses)
+ *   - `mock-reader.ts`    — dev, no hardware (keyboard / console trigger)
+ *   - `web-nfc-reader.ts` — Web NFC / NDEFReader, laptop/phone dev (PR3)
+ *   - `serial-reader.ts`  — /dev/ttyNFC via main-process HAL + IPC (PR4)
+ *
+ * The reader emits a RAW credential; hashing/authorization (and the optional
+ * PIN second factor) is the store's job (see `authorize.ts`), so raw ids never
+ * leave this layer (KYC-free).
+ */
+
+import type { AccessRole } from '@bitSpire/state-machine'
+
+export type { AccessRole }
+
+export type AccessReaderKind = 'qr-npub' | 'mock' | 'nfc-web' | 'nfc-serial'
+
+/**
+ * A raw credential captured by a reader. Discriminated union so new factors
+ * are additive:
+ *   - `npub`      — prototype QR badge (this PR)
+ *   - `uid`       — NFC card UID (PR4)
+ *   - `challenge` — card-signed nonce, challenge-response (PR5)
+ */
+export type AccessScan =
+  | { kind: 'npub'; npub: string }
+  | { kind: 'uid'; uid: string }
+  | { kind: 'challenge'; pubkey: string; nonce: string; sig: string }
+
+export interface AccessReaderStartOptions {
+  /** Called with each captured credential. */
+  onScan: (scan: AccessScan) => void
+  /** Non-fatal capture error (e.g. a frame decode glitch). */
+  onError?: (error: unknown) => void
+  /**
+   * The <video> element a camera reader renders into. Required by camera
+   * readers (qr-npub); ignored by readers with no viewfinder (mock, NFC).
+   */
+  video?: HTMLVideoElement
+}
+
+/** Releases the reader (camera stream, event listeners, serial handle). Idempotent. */
+export type StopCapture = () => void
+
+export interface AccessReader {
+  readonly kind: AccessReaderKind
+  /** Short human label for status/debug UI. */
+  readonly label: string
+  /** Whether this reader can run in the current environment. */
+  isAvailable(): Promise<boolean>
+  /** Begin capturing; resolves once the reader is live. */
+  start(opts: AccessReaderStartOptions): Promise<StopCapture>
+}
diff --git a/apps/machine/src/stores/atm.ts b/apps/machine/src/stores/atm.ts
index db1a124..28eb75b 100644
--- a/apps/machine/src/stores/atm.ts
+++ b/apps/machine/src/stores/atm.ts
@@ -8,7 +8,9 @@ import {
   type ActorRefFrom,
   type SnapshotFrom,
   type ATMMachine,
+  type AccessRole,
 } from '@bitSpire/state-machine'
+import type { AccessControlConfig } from '@/types/electron'
 import { initializeLightningServices, fetchBtcPrice } from '@/services/lightning'
 import { classifyInitError } from '@/services/init-error'
 import { startOperatorConfigService, type OperatorConfigService } from '@/services/operator-config'
@@ -291,6 +293,18 @@ export const useAtmStore = defineStore('atm', () => {
   // is in flight (settlement still arrives via the normal invoice watcher).
   const nfcStatus = ref<{ state: string; message?: string } | null>(null)
   const boltCardProcessing = ref(false)
+  // Access-control gate config (ADR-003). Defaults disabled → the machine's
+  // `locked` state bypasses straight to `idle` (behaviour identical to no gate).
+  // Populated from RuntimeConfig.accessControl in initializeForProduction.
+  const accessControl = ref<AccessControlConfig>({
+    enabled: false,
+    devUnlock: false,
+    openEnrollment: false,
+    salt: 'bitspire-access-v1',
+    allowList: [],
+  })
+  // Build/dev bypass — opens the gate even when enabled (browser dev / CI).
+  const accessBypassFlag = import.meta.env.VITE_SKIP_ACCESS_GATE === 'true'
   const fiatCode = ref('USD')
   // Defaults are 0 — the operator's fee config (received via Nostr
   // kind-30078 `bitspire-fees:<atm_pubkey>` envelope from satmachineadmin)
@@ -421,6 +435,11 @@ export const useAtmStore = defineStore('atm', () => {
 
   const isIdle = computed(() => currentState.value === 'idle')
 
+  // ADR-003: the machine is sitting at the access gate. When the gate is
+  // disabled this is never true (the `locked` state bypasses to `idle` on
+  // start), so App.vue's LockedView branch never renders on a non-access machine.
+  const isLocked = computed(() => currentState.value === 'locked')
+
   const isCashIn = computed(() => {
     const state = snapshot.value?.value
     return typeof state === 'object' && 'cashIn' in state
@@ -448,6 +467,8 @@ export const useAtmStore = defineStore('atm', () => {
       currency: fiatCode.value,
       cashInFeeFraction: cashInFeeFraction.value,
       cashOutFeeFraction: cashOutFeeFraction.value,
+      accessControlEnabled: accessControl.value.enabled,
+      accessBypassFlag,
     })
     actor.value = createActor(machine)
 
@@ -1183,6 +1204,19 @@ export const useAtmStore = defineStore('atm', () => {
     const runtimeFiatCode = runtimeConfig.fiatCode || 'USD'
     fiatCode.value = runtimeFiatCode
 
+    // Access-control gate (ADR-003). Must be set BEFORE the machine is built
+    // (initialize() reads accessControl.value to seed the `locked` state).
+    if (runtimeConfig.accessControl) {
+      accessControl.value = runtimeConfig.accessControl
+      if (runtimeConfig.accessControl.enabled) {
+        console.log(
+          `[ATM] Access control ENABLED (openEnrollment=${runtimeConfig.accessControl.openEnrollment}, ` +
+            `allowList=${runtimeConfig.accessControl.allowList.length} entries, ` +
+            `devUnlock=${runtimeConfig.accessControl.devUnlock})`
+        )
+      }
+    }
+
     // Load persisted operator fee config (aiolabs/lamassu-next#57). If no
     // config has ever been applied (fresh ATM, pre-operator-publish),
     // enter the 'awaiting-fees' maintenance state — UI shows the operator
@@ -1491,6 +1525,48 @@ export const useAtmStore = defineStore('atm', () => {
     actor.value.send(event)
   }
 
+  // === Access control (ADR-003) ===
+
+  /**
+   * Audit stub — records an access decision. PR1 logs only (hashed id, never a
+   * raw credential); a fast-follow persists to state.db and optionally a Nostr
+   * event (see ADR-003).
+   */
+  function recordAccessAudit(outcome: {
+    result: 'granted' | 'denied'
+    role?: AccessRole
+    credentialIdHash: string
+    reason?: string
+  }) {
+    console.info('[Access] audit', {
+      result: outcome.result,
+      role: outcome.role ?? null,
+      // Truncate the hash in logs — it's already non-reversible, but no need to
+      // splash the full value across the journal.
+      credentialIdHash: outcome.credentialIdHash.slice(0, 12),
+      reason: outcome.reason ?? null,
+      at: Date.now(),
+    })
+  }
+
+  /** Grant terminal access after a credential (and any PIN) is authorized. */
+  function grantAccess(role: AccessRole, credentialIdHash: string) {
+    recordAccessAudit({ result: 'granted', role, credentialIdHash })
+    send({ type: 'ACCESS_GRANTED', role, credentialIdHash })
+  }
+
+  /** Reject an access attempt; the machine stays locked and shows the reason. */
+  function denyAccess(reason: string, credentialIdHash = '') {
+    recordAccessAudit({ result: 'denied', credentialIdHash, reason })
+    send({ type: 'ACCESS_DENIED', reason })
+  }
+
+  /** Runtime dev/operator unlock (gated by the machine's devUnlockAllowed guard). */
+  function devUnlock() {
+    recordAccessAudit({ result: 'granted', role: 'operator', credentialIdHash: 'dev-unlock' })
+    send({ type: 'DEV_UNLOCK' })
+  }
+
   // Convenience methods for common events
   function selectCashIn() {
     send({ type: 'SELECT_CASH_IN' })
@@ -1641,6 +1717,13 @@ export const useAtmStore = defineStore('atm', () => {
     simulateBoltCardTap,
     simulateBoltCardReceive,
 
+    // Access control (ADR-003)
+    accessControl,
+    isLocked,
+    grantAccess,
+    denyAccess,
+    devUnlock,
+
     // Actions
     initialize,
     initializeWithLightning,
diff --git a/apps/machine/src/types/electron.d.ts b/apps/machine/src/types/electron.d.ts
index 0e5846d..95425f6 100644
--- a/apps/machine/src/types/electron.d.ts
+++ b/apps/machine/src/types/electron.d.ts
@@ -2,6 +2,26 @@
  * Type declarations for Electron API exposed via preload
  */
 
+import type { AllowListEntry } from '../services/access/authorize'
+
+/**
+ * Access-control config (ADR-003). Loaded by the main process from env +
+ * an optional /var/lib/bitspire/access.json. `enabled` defaults false, so a
+ * machine with no access config behaves exactly as before.
+ */
+export interface AccessControlConfig {
+  /** Master switch for the badge-to-enter gate. */
+  enabled: boolean
+  /** Allow the runtime dev/operator unlock gesture on the locked screen. */
+  devUnlock: boolean
+  /** Prototype: admit any valid npub when the allow-list has no match. */
+  openEnrollment: boolean
+  /** Per-machine salt for hashing credentials/PINs. */
+  salt: string
+  /** Authorized identities (hashed). Empty in open-enrollment prototype mode. */
+  allowList: AllowListEntry[]
+}
+
 export interface RuntimeConfig {
   relayUrl: string
   /** LNbits nostr-transport server pubkey (hex, 64 chars). */
@@ -17,6 +37,8 @@ export interface RuntimeConfig {
   maintenanceMode: boolean
   /** Operator branding override loaded from /var/lib/bitspire/branding/. Null when no override. */
   branding: BrandingConfig | null
+  /** Access-control gate config (ADR-003). Always present; `enabled` defaults false. */
+  accessControl: AccessControlConfig
 }
 
 /** Operator branding config. Wire payload from Electron IPC; renderer applies via useBranding(). */
diff --git a/apps/machine/src/views/LockedView.vue b/apps/machine/src/views/LockedView.vue
new file mode 100644
index 0000000..90c4ac0
--- /dev/null
+++ b/apps/machine/src/views/LockedView.vue
@@ -0,0 +1,316 @@
+<script setup lang="ts">
+/**
+ * Access gate — "present your badge" screen (ADR-003).
+ *
+ * Shown when the machine is healthy but locked (App.vue's `isLocked` branch).
+ * Until NFC hardware exists, the PROTOTYPE reader is the camera: the user
+ * shows a QR encoding their npub. On decode we authorize() it (optionally
+ * behind a PIN) and grant/deny access on the state machine. A mock reader
+ * (F9 / console) is the keyboard fallback when no camera is present.
+ *
+ * Reader lifecycle lives here (this view owns the <video>), mirroring
+ * PairingWizard; the store owns the machine events (grant/deny/devUnlock).
+ */
+import { computed, onMounted, onUnmounted, ref, shallowRef } from 'vue'
+import { useAtmStore } from '@/stores/atm'
+import { useBranding } from '@/composables/useBranding'
+import { Button } from '@/components/ui/button'
+import ColorModeToggle from '@/components/ColorModeToggle.vue'
+import { ScanLine } from 'lucide-vue-next'
+import {
+  availableAccessReaders,
+  authorize,
+  type AccessReader,
+  type AccessScan,
+  type StopCapture,
+} from '@/services/access'
+
+const atmStore = useAtmStore()
+const { logoUrl, title } = useBranding()
+
+const videoEl = ref<HTMLVideoElement | null>(null)
+const reader = shallowRef<AccessReader | null>(null)
+let stopCapture: StopCapture | null = null
+
+// Two-step PIN flow: set when a scanned credential needs a PIN. Holds the
+// original scan so the PIN can be verified against the same identity.
+const pinPending = ref<AccessScan | null>(null)
+const pinEntry = ref('')
+const statusMessage = ref('')
+
+const denyReason = computed(() => atmStore.snapshot?.context.accessDenyReason ?? null)
+const showDevUnlock = computed(() => atmStore.accessControl.devUnlock)
+
+// The camera stays ON (always ready to scan), but the live stream is HIDDEN
+// behind a branded overlay by default — showing a moving camera feed to every
+// passer-by is distracting. Tapping the overlay reveals the preview so the
+// person can aim their QR; after 90s of no interaction we hide it again.
+const showStream = ref(false)
+const INACTIVITY_MS = 90_000
+let idleTimer: ReturnType<typeof setTimeout> | null = null
+function clearIdle() {
+  if (idleTimer) {
+    clearTimeout(idleTimer)
+    idleTimer = null
+  }
+}
+/** Hide the stream (and drop any half-entered PIN) back to the overlay. */
+function returnToOverlay() {
+  clearIdle()
+  showStream.value = false
+  pinPending.value = null
+  pinEntry.value = ''
+  handling = false
+}
+function armIdle() {
+  clearIdle()
+  idleTimer = setTimeout(returnToOverlay, INACTIVITY_MS)
+}
+/** Reveal the live preview and (re)start the inactivity countdown. */
+function revealStream() {
+  showStream.value = true
+  armIdle()
+}
+/** Any user interaction while the stream/PIN is up keeps it awake. */
+function noteInteraction() {
+  if (showStream.value || pinPending.value) armIdle()
+}
+
+// Camera-preview rotation is a per-hardware-mount value (the batm3's webcam
+// sits differently from the Sintra's). Rather than hardcode-and-rebuild to
+// find it, make it adjustable live: press "r" to rotate 90° per press. The
+// choice persists (localStorage on the writable root) so it survives restarts,
+// and QR decode is rotation-invariant so this is purely cosmetic.
+const ROTATION_KEY = 'access-preview-rotation'
+const previewRotation = ref(((Number(localStorage.getItem(ROTATION_KEY)) % 360) + 360) % 360)
+const rotationClass = computed(
+  () =>
+    ({ 0: '', 90: 'rotate-90', 180: 'rotate-180', 270: '-rotate-90' })[previewRotation.value] ?? ''
+)
+function cyclePreviewRotation() {
+  previewRotation.value = (previewRotation.value + 90) % 360
+  localStorage.setItem(ROTATION_KEY, String(previewRotation.value))
+}
+function onRotateKey(e: KeyboardEvent) {
+  noteInteraction()
+  // Only an operator/dev may re-orient the preview (gated like the unlock).
+  if (!showDevUnlock.value) return
+  if (e.key === 'r' || e.key === 'R') cyclePreviewRotation()
+}
+
+async function teardown() {
+  if (stopCapture) {
+    try {
+      stopCapture()
+    } catch {
+      /* idempotent */
+    }
+    stopCapture = null
+  }
+}
+
+async function startReader() {
+  await teardown()
+  const [first] = await availableAccessReaders()
+  reader.value = first ?? null
+  if (!first) {
+    statusMessage.value = 'No reader available.'
+    return
+  }
+  try {
+    stopCapture = await first.start({
+      video: first.kind === 'qr-npub' ? (videoEl.value ?? undefined) : undefined,
+      onScan: handleScan,
+      onError: (e) => console.warn('[Access] capture glitch:', e),
+    })
+  } catch (e) {
+    statusMessage.value =
+      e instanceof Error ? e.message : 'Could not start the reader.'
+  }
+}
+
+let handling = false
+async function handleScan(scan: AccessScan) {
+  if (handling) return
+  handling = true
+  // A detected QR is an interaction — surface the preview so the result
+  // (grant / PIN prompt / denial) is visible even if the overlay was up.
+  revealStream()
+  await teardown() // reader off while we decide
+
+  const cfg = atmStore.accessControl
+  const outcome = await authorize(scan, cfg.allowList, {
+    salt: cfg.salt,
+    openEnrollment: cfg.openEnrollment,
+  })
+
+  if (outcome.status === 'granted') {
+    atmStore.grantAccess(outcome.role, outcome.credentialIdHash)
+    return // machine leaves `locked`; view unmounts
+  }
+  if (outcome.status === 'pin-required') {
+    pinPending.value = scan
+    pinEntry.value = ''
+    statusMessage.value = ''
+    handling = false
+    return
+  }
+  // denied — show reason and resume scanning
+  atmStore.denyAccess(outcome.reason, outcome.credentialIdHash)
+  handling = false
+  await startReader()
+}
+
+async function submitPin() {
+  const scan = pinPending.value
+  if (!scan) return
+  const cfg = atmStore.accessControl
+  const outcome = await authorize(scan, cfg.allowList, {
+    salt: cfg.salt,
+    openEnrollment: cfg.openEnrollment,
+    pin: pinEntry.value,
+  })
+  if (outcome.status === 'granted') {
+    atmStore.grantAccess(outcome.role, outcome.credentialIdHash)
+    return
+  }
+  // wrong PIN (or anything else) — back to scanning
+  atmStore.denyAccess(outcome.status === 'denied' ? outcome.reason : 'access denied')
+  pinPending.value = null
+  pinEntry.value = ''
+  handling = false
+  await startReader()
+}
+
+function cancelPin() {
+  pinPending.value = null
+  pinEntry.value = ''
+  handling = false
+  void startReader()
+}
+
+function pressDigit(d: string) {
+  if (pinEntry.value.length < 12) pinEntry.value += d
+}
+function backspacePin() {
+  pinEntry.value = pinEntry.value.slice(0, -1)
+}
+
+onMounted(() => {
+  startReader()
+  window.addEventListener('keydown', onRotateKey)
+})
+onUnmounted(() => {
+  clearIdle()
+  teardown()
+  window.removeEventListener('keydown', onRotateKey)
+})
+</script>
+
+<template>
+  <div
+    class="relative flex flex-1 flex-col items-center justify-center gap-10 bg-background p-8 text-foreground"
+    @pointerdown="noteInteraction"
+  >
+    <!-- Light/dark toggle — shared kiosk-sized component -->
+    <ColorModeToggle class="absolute right-4 top-4 z-10" />
+
+    <!-- Brand: logo + title only, colours from the active theme (branding.json) -->
+    <div class="flex flex-col items-center gap-4">
+      <img
+        v-if="logoUrl"
+        :src="logoUrl"
+        alt=""
+        class="h-[16vh] max-h-44 w-auto object-contain"
+      />
+      <h1 class="text-3xl font-bold tracking-tight lg:text-5xl">{{ title }}</h1>
+    </div>
+
+    <!-- PIN entry (second factor) -->
+    <div v-if="pinPending" class="flex flex-col items-center gap-6">
+      <p class="text-lg text-muted-foreground lg:text-2xl">Enter your PIN</p>
+      <div class="font-mono text-4xl tracking-[0.5em] text-foreground">
+        {{ '•'.repeat(pinEntry.length) || '—' }}
+      </div>
+      <div class="grid grid-cols-3 gap-3">
+        <Button
+          v-for="d in ['1', '2', '3', '4', '5', '6', '7', '8', '9']"
+          :key="d"
+          size="kiosk-icon"
+          variant="outline"
+          @click="pressDigit(d)"
+          >{{ d }}</Button
+        >
+        <Button size="kiosk-icon" variant="ghost" @click="backspacePin">⌫</Button>
+        <Button size="kiosk-icon" variant="outline" @click="pressDigit('0')">0</Button>
+        <Button size="kiosk-icon" variant="default" @click="submitPin">✓</Button>
+      </div>
+      <Button variant="ghost" @click="cancelPin">Cancel</Button>
+    </div>
+
+    <!-- Camera viewfinder (npub QR badge). The camera keeps running underneath;
+         an opaque, pressable overlay hides the live feed until someone taps. -->
+    <template v-else>
+      <div class="flex flex-col items-center gap-5">
+        <div
+          class="relative overflow-hidden rounded-3xl border-4 border-primary bg-black shadow-xl"
+          style="width: min(72vw, 26rem); aspect-ratio: 1 / 1"
+        >
+          <!-- Rotation is adjustable live (press "r"); persisted per machine. -->
+          <video
+            ref="videoEl"
+            class="h-full w-full object-cover"
+            :class="rotationClass"
+            muted
+            autoplay
+            playsinline
+          ></video>
+          <div class="pointer-events-none absolute inset-6 rounded-2xl border-2 border-primary/50"></div>
+
+          <!-- Default overlay: hides the stream + invites a tap to reveal it. -->
+          <button
+            v-if="!showStream"
+            class="absolute inset-0 flex flex-col items-center justify-center gap-4 bg-card text-card-foreground transition-colors hover:bg-card/90"
+            @click="revealStream"
+          >
+            <ScanLine class="size-16 text-primary" />
+            <span class="text-xl font-semibold lg:text-2xl">Tap to scan</span>
+            <span class="max-w-[80%] text-center text-sm text-muted-foreground lg:text-base">
+              Show the camera to scan your access QR
+            </span>
+          </button>
+        </div>
+
+        <template v-if="showStream">
+          <p class="text-2xl font-semibold text-foreground lg:text-3xl">Scan to enter</p>
+          <p class="max-w-md text-center text-base text-muted-foreground lg:text-xl">
+            Present your access QR to the camera
+          </p>
+          <p v-if="denyReason" class="text-lg font-medium text-destructive lg:text-xl">
+            {{ denyReason }}
+          </p>
+          <p v-else-if="statusMessage" class="text-base text-muted-foreground">
+            {{ statusMessage }}
+          </p>
+        </template>
+      </div>
+
+      <div v-if="showDevUnlock" class="mt-2 flex flex-col items-center gap-1">
+        <Button
+          variant="ghost"
+          size="sm"
+          class="text-muted-foreground opacity-40 transition-opacity hover:opacity-100"
+          @click="atmStore.devUnlock()"
+        >
+          Dev unlock
+        </Button>
+        <button
+          class="text-xs text-muted-foreground opacity-40 transition-opacity hover:opacity-100"
+          @click="cyclePreviewRotation"
+        >
+          press “r” to rotate camera · {{ previewRotation }}°
+        </button>
+      </div>
+    </template>
+  </div>
+</template>
diff --git a/deploy/nixos/access.example.json b/deploy/nixos/access.example.json
new file mode 100644
index 0000000..7f20fcf
--- /dev/null
+++ b/deploy/nixos/access.example.json
@@ -0,0 +1,5 @@
+{
+  "enabled": true,
+  "openEnrollment": true,
+  "devUnlock": true
+}
diff --git a/deploy/nixos/provision-access.sh b/deploy/nixos/provision-access.sh
new file mode 100755
index 0000000..72dd12b
--- /dev/null
+++ b/deploy/nixos/provision-access.sh
@@ -0,0 +1,69 @@
+#!/usr/bin/env bash
+# Provision the access-control gate (ADR-003) to a deployed bitSpire ATM.
+# Pushes an access.json to /var/lib/bitspire/ and restarts the service, so the
+# gate can be toggled on a machine without an image rebuild (mirrors
+# provision-branding.sh). Env defaults are overridden by whatever this file sets.
+#
+# Usage:
+#   bash provision-access.sh <access.json>                    # SSH to localhost:2222 (QEMU)
+#   bash provision-access.sh <access.json> 192.168.1.50       # a real ATM on the LAN
+#   bash provision-access.sh <access.json> 192.168.1.50 22    # custom SSH port
+#
+# access.json schema (all keys optional; omitted keys fall back to env/defaults):
+#   {
+#     "enabled": true,           // master switch for the gate
+#     "openEnrollment": true,    // prototype: admit any valid npub
+#     "devUnlock": true,         // allow the on-screen dev/operator unlock
+#     "salt": "per-machine",     // hashing salt (provision a real one for prod)
+#     "allowList": [             // authorized identities (hashed); empty in open mode
+#       { "idHash": "<hashId(hexpubkey,salt)>", "role": "user", "pinHash": "<hashPin(pin,salt)>" }
+#     ]
+#   }
+#
+# To DISABLE the gate again: push a file with {"enabled": false} (or delete
+# /var/lib/bitspire/access.json on the machine) and restart.
+set -euo pipefail
+
+ACCESS_FILE="${1:-}"
+ATM_HOST="${2:-localhost}"
+ATM_SSH_PORT="${3:-2222}"
+ATM_USER="bitspire"
+REMOTE_FILE="/var/lib/bitspire/access.json"
+
+if [ -z "$ACCESS_FILE" ]; then
+    echo "Usage: $0 <access.json> [host] [port]" >&2
+    echo "       $0 ./access.json                       (QEMU on localhost:2222)" >&2
+    echo "       $0 ./access.json 192.168.1.50          (real ATM)" >&2
+    exit 1
+fi
+
+if [ ! -f "$ACCESS_FILE" ]; then
+    echo "ERROR: access file not found: $ACCESS_FILE" >&2
+    exit 1
+fi
+
+# Fail fast on malformed JSON before touching the machine.
+if command -v jq >/dev/null 2>&1; then
+    jq empty "$ACCESS_FILE" || { echo "ERROR: $ACCESS_FILE is not valid JSON" >&2; exit 1; }
+fi
+
+echo "=== Provisioning access gate to $ATM_HOST:$ATM_SSH_PORT ==="
+echo "Local file : $ACCESS_FILE"
+echo "Remote file: $REMOTE_FILE"
+cat "$ACCESS_FILE"
+echo ""
+
+# Copy over SSH. --rsync-path=sudo because /var/lib/bitspire is owned by the
+# bitspire service user, not the SSH user.
+rsync -avz \
+    --rsync-path="sudo rsync" \
+    -e "ssh -o StrictHostKeyChecking=no -p $ATM_SSH_PORT" \
+    "$ACCESS_FILE" \
+    "$ATM_USER@$ATM_HOST:$REMOTE_FILE"
+
+# Restart so loadAccessControl() re-reads the file.
+ssh -o StrictHostKeyChecking=no -p "$ATM_SSH_PORT" "$ATM_USER@$ATM_HOST" \
+    "sudo systemctl restart bitspire"
+
+echo ""
+echo "=== Access gate provisioned. Service restarted. ==="
diff --git a/docs/adr/003-nfc-access-control-layer.md b/docs/adr/003-nfc-access-control-layer.md
new file mode 100644
index 0000000..02a32f1
--- /dev/null
+++ b/docs/adr/003-nfc-access-control-layer.md
@@ -0,0 +1,201 @@
+# ADR-003: NFC Access-Control Layer (badge-to-enter) + Developer Bypass
+
+**Status:** Accepted
+**Date:** 2026-07-29
+**Context:** batm3 gaining a physical access layer — an NFC card must be presented to unlock the machine before anyone can transact. Reader hardware is not yet on hand; this ADR defines the direction and a non-breaking skeleton that is fully testable without it.
+
+## Decision
+
+1. **Add a top-level `locked` state to the ATM state machine, and make it the initial state.** It sits *below* the existing initialization gates (`unpaired` / `awaiting-fees` / `maintenance` / `signer-unreachable`, which live in `App.vue`). A healthy, paired machine boots into `locked` and only reveals `idle` (Buy/Sell) after an access grant.
+
+2. **Access control is opt-in via runtime config (`accessControl.enabled`, default `false`).** When disabled, the machine behaves exactly as today (boots straight to `idle`). This makes the whole feature non-breaking for the current test unit and for production ATMs, and lets a half-built access layer never brick a working box. This is the single most important constraint on the design.
+
+3. **The reader lives behind an `AccessReader` abstraction that mirrors the existing `PairingSource` seam.** First implementation is a `MockAccessReader` (dev button / hotkey), so the locked→idle→transaction path is exercisable today with zero hardware. Web NFC and serial-NFC implementations follow.
+
+4. **Credential model is a discriminated union with an explicit upgrade path.** v1 = card UID matched against a hashed allow-list. v2 = challenge-response (card-held key signs a machine nonce), verified against an operator-authorized set. Ship v1; design the types so v2 is additive.
+
+5. **Three-tier developer bypass**, following existing conventions: a build flag (`VITE_SKIP_ACCESS_GATE`), the config disable (`accessControl.enabled=false`), and a runtime operator/dev unlock gesture that dispatches a synthetic grant.
+
+6. **Authorization is owned by the machine operator, not the SaaS operator** — consistent with [ADR-002](./002-remote-access-and-fleet-management.md). The card allow-list is authorized by the operator key (the [#42](https://git.atitlan.io/aiolabs/bitspire/issues/42) allow-list mechanism), local first, operator-synced later. When access control is *enabled* and the reader is absent/broken, the machine **fails closed** (with the operator/dev unlock as the escape hatch); when *disabled*, reader state is irrelevant.
+
+7. **Every grant/deny is audited** to `state.db` (hashed credential + timestamp + role + outcome), with optional later publication as a Nostr event. No PII, consistent with the KYC-free principle.
+
+## Context
+
+### What this is (and what it is not)
+
+This is the **end-user physical access plane**: a person must badge in to use the machine. It is distinct from the three planes in [ADR-002](./002-remote-access-and-fleet-management.md) — it is *not* the operator's SSH/NetBird recovery plane, and *not* the SaaS payment plane. It shares one idea with ADR-002: **the machine operator owns who is authorized**, expressed through the operator key / #42 allow-list.
+
+### Why the codebase is well-shaped for this
+
+Three seams already exist; we extend them rather than invent:
+
+- **The idle→transaction transition is unguarded.** `packages/state-machine/src/machine.ts` starts at `initial: 'idle'` (~L431) and `idle` moves to `cashIn`/`cashOut` via plain `SELECT_CASH_IN` / `SELECT_CASH_OUT` transitions with no guards (~L457-464). Inserting a `locked` predecessor state is a localized change.
+- **`PairingSource` is a reader abstraction designed to grow.** Its doc (`apps/machine/src/services/pairing/types.ts`) explicitly anticipates *"an NFC reader or a HAL barcode scanner… a HAL-scanner source can be added the same way without touching the wizard."* `AccessReader` mirrors it: `qr-source.ts` / `nfc-source.ts` → `mock-reader.ts` / `web-nfc-reader.ts` / `serial-reader.ts`.
+- **Dev-flag and config conventions are established.** `import.meta.env.VITE_* === 'true'` (e.g. `VITE_MAINTENANCE_MODE`, `VITE_FORCE_MOCK`), plus Electron `get-config` fields that the renderer reads (`electron/main.ts` L280–312: `maintenanceMode`, `branding`). A new `accessControl` config field and a `VITE_SKIP_ACCESS_GATE` flag follow the same shape.
+
+### Hardware reality check (important)
+
+The batm3 already exposes an NFC device, but it is **serial**: `deploy/nixos/hardware/batm3.nix` L154 maps udev serial `A9ZF8ELY` → `/dev/ttyNFC`. The *existing* `pairing/nfc-source.ts` uses **Web NFC** (`NDEFReader`), which drives a phone/laptop NFC radio, **not** a serial reader. So the real batm3 access reader needs a **main-process serial driver** (HAL-style, per [ADR-001](./001-hal-architecture.md)) exposing card events to the renderer over IPC — the Web NFC path is only useful for laptop/phone dev. This ADR keeps that driver as a clearly-scoped later PR so the skeleton doesn't pretend the scaffold "just works" on the panel.
+
+## Architecture
+
+### Boot / render layering
+
+```
+Electron get-config ─┐
+                     ▼
+App.vue init gates (unchanged):
+  unpaired? → PairingWizard
+  initError (maintenance / awaiting-fees / signer-unreachable)? → maintenance screen
+  else ▼
+State machine (paired + healthy):
+  ┌───────────────────────────────────────────────┐
+  │  locked  ──ACCESS_GRANTED──▶  idle             │  ← NEW initial state
+  │    ▲                          │  SELECT_CASH_* │
+  │    │ re-lock (session end /    ▼               │
+  │    │ inactivity / complete)   cashIn / cashOut │
+  │    └──────────────────────────┘               │
+  └───────────────────────────────────────────────┘
+        (when accessControl.enabled === false,
+         `locked` immediately `always`-bypasses to `idle`)
+```
+
+The access gate is strictly below App.vue's init gates: a machine that is unpaired or in maintenance never reaches `locked`.
+
+### 1. State machine (`packages/state-machine`)
+
+- New top-level state `locked`, `initial: 'locked'`.
+- New events on the machine's event union: `ACCESS_GRANTED` (carries an authorized `CardCredential` + resolved role), `ACCESS_DENIED` (carries a reason), `DEV_UNLOCK`.
+- `locked` transitions:
+  - `always: [{ guard: 'accessBypass', target: 'idle' }]` — instant pass-through when disabled/bypassed (no UI flicker; the view is gated on the same predicate).
+  - `on: { ACCESS_GRANTED: { target: 'idle', actions: ['startSession', 'recordAccessGrant'] }, ACCESS_DENIED: { actions: 'recordAccessDeny' }, DEV_UNLOCK: { guard: 'devUnlockAllowed', target: 'idle', actions: 'startDevSession' } }`.
+- Re-lock: the existing `complete` auto-return (currently 60s → `idle`) and the inactivity timeouts (`INACTIVITY_TIMEOUT`/`TIMEOUT_MS`, ~L422-429) target `locked` instead of `idle`. Because `locked` `always`-bypasses when disabled, this is one code path for both modes.
+- Purity: the state-machine package must not read Vite env. `accessControl.enabled` and the bypass boolean are passed in as **actor input → context** (`context.accessControlEnabled`, `context.accessBypass`); guard `accessBypass` reads context only. New context fields: `accessControlEnabled`, `accessBypass`, `session` (`{ role, grantedAt, credentialIdHash } | null`).
+- Guards: `accessBypass`, `devUnlockAllowed`. Actions: `startSession`, `startDevSession`, `recordAccessGrant`, `recordAccessDeny`, and `resetContext` extended to clear `session`.
+
+### 2. Config plumbing
+
+- `apps/machine/src/types/electron.d.ts` — extend `RuntimeConfig` (L5) with:
+  ```ts
+  accessControl: {
+    enabled: boolean            // default false
+    devUnlock: boolean          // allow the runtime operator/dev unlock gesture
+    // v2: allowListSource, challengeRequired, …
+  }
+  ```
+- `apps/machine/electron/main.ts` — the `get-config` handler (L280) returns `accessControl`, sourced from env for now (`ACCESS_CONTROL_ENABLED === 'true'`, `VITE_SKIP_ACCESS_GATE` → forces `enabled:false`), later from a provisioned file under `/var/lib/bitspire/` alongside branding.
+- `apps/machine/.env.example` — document `VITE_SKIP_ACCESS_GATE=true` (browser/dev straight to idle) and `ACCESS_CONTROL_ENABLED`.
+
+### 3. Reader abstraction (`apps/machine/src/services/access/`)
+
+Mirrors `services/pairing/`:
+
+```
+services/access/
+  types.ts          # AccessReader, CardCredential (union), AccessRole, StopCapture
+  mock-reader.ts    # PR1 — fires a card event on demand (dev button / hotkey)
+  web-nfc-reader.ts # PR3 — NDEFReader, dev on laptop/phone
+  serial-reader.ts  # PR4 — /dev/ttyNFC via main-process HAL + IPC
+  authorize.ts      # allow-list check + role resolution (hashed UID v1)
+  index.ts          # availableAccessReaders(): AccessReader[]
+  __tests__/
+```
+
+```ts
+export type AccessRole = 'user' | 'operator'
+
+export type CardCredential =
+  | { kind: 'uid'; uidHash: string }                                  // v1
+  | { kind: 'challenge'; pubkey: string; nonce: string; sig: string } // v2 (seam)
+
+export interface AccessReader {
+  readonly kind: 'mock' | 'nfc-web' | 'nfc-serial'
+  readonly label: string
+  isAvailable(): Promise<boolean>
+  start(opts: {
+    onCard: (cred: CardCredential) => void
+    onError?: (e: unknown) => void
+  }): Promise<StopCapture>
+}
+```
+
+### 4. Renderer wiring
+
+- `apps/machine/src/views/LockedView.vue` (new) — the badge-in screen. Shows brand/logo + "Present your card", a live reader status, and (when `accessControl.devUnlock`) a discreet operator/dev unlock affordance (hidden long-press corner, or a button on the existing debug bar).
+- `apps/machine/src/App.vue` — add a `locked` render branch mirroring the `PairingWizard` branch (L179) and the `initError` branch (L183): `<LockedView v-else-if="atmStore.isLocked" />`, then the existing `<router-view>` only when unlocked. Keeps rendering state-driven and matches the current shape.
+- `apps/machine/src/stores/atm.ts` —
+  - `createActor(machine, { input: { accessControlEnabled, accessBypass } })` at the existing `createActor(machine)` site (L452), seeded from `RuntimeConfig`.
+  - `isLocked` computed off the snapshot (peer of `isIdle`, ~L422).
+  - `grantAccess(cred, role)` / `denyAccess(reason)` / `devUnlock()` that `send({ type: 'ACCESS_GRANTED' | 'ACCESS_DENIED' | 'DEV_UNLOCK', … })` (peers of `selectCashIn` at L1382, using the existing `send` at L1378).
+  - On init, when `accessControl.enabled`, subscribe to `availableAccessReaders()[0]`; on `onCard`, run `authorize()` → `grantAccess`/`denyAccess`. When disabled, do nothing (machine `always`-bypasses).
+
+### 5. Audit
+
+- Add `recordAccessEvent({ credentialIdHash, role, outcome, at })` alongside the existing state.db handlers (`state:record-transaction` etc. in `electron/main.ts`, exposed via `preload.ts`). v1 writes locally; a later PR can mirror to a replaceable Nostr event.
+
+### Session semantics (decided)
+
+**One badge = one transaction-scoped session.** A grant unlocks `idle`, the user runs a single transaction (Buy or Sell), and the machine re-locks on `complete`, on inactivity, or on an explicit "Done". The `session` context field is deliberately shaped as a general access session (`{ role, grantedAt, credentialIdHash }`), not a transaction handle, because this terminal may later handle **non-transaction functions** — so "unlock the terminal" and "authorize a transaction" stay separate concepts.
+
+**Step-up authorization (future seam, not in PR1).** The badge tap grants *terminal access*; a specific sensitive action can independently *request re-authorization* — e.g. "tap your phone" or "enter a PIN" — without conflating the two. This is why the credential model is a union and the machine carries a `session` rather than a boolean "unlocked": a later `REQUIRE_STEPUP` event can gate an individual action against a fresh credential/PIN while the terminal session stays open. PR1 ships only the entry gate; step-up is a documented extension.
+
+## Alternatives considered
+
+- **Gate between `idle` and the transaction** (idle visible, tap requires a card). Rejected: the requirement is "gain access to the exchange" — the whole machine should be locked, not just the transact button. A `locked` predecessor matches the mental model and gives a clean re-lock boundary.
+- **Web NFC only** (reuse `nfc-source.ts` as-is). Rejected: the batm3 reader is serial (`ttyNFC`); Web NFC can't drive it. Web NFC stays a dev-only convenience.
+- **Fail-open by default** (no card → allow). Rejected for an access-control feature; but note the *disabled* default sidesteps this — access is simply off until an operator turns it on, at which point it fails **closed**.
+- **OS/kiosk-level lock** (lock the desktop, not the app). Rejected: too coarse, no per-transaction audit, no role model, and it fights the existing state-driven UI.
+- **UID allow-list as the permanent model.** Rejected as an endpoint (UIDs clone trivially) but accepted as v1 behind a union type, so challenge-response is additive.
+
+## Security considerations
+
+- **UID cloning** — card UIDs are not secret and are cloneable; v1 is "better than nothing" and is explicitly labeled upgradeable. The v2 challenge-response path (card signs a machine nonce) is the real security boundary; design the credential union and the `authorize()` seam for it now.
+- **Data at rest** — store only a salted hash of the credential id; never raw UIDs or any PII (KYC-free). Never log a card secret or nsec (repo security priority #1).
+- **Fail-closed when enabled** — reader absent/broken + `enabled` ⇒ locked, escape hatch = operator/dev unlock. Reader problems on a *disabled* machine are inert.
+- **Operator ownership** — authorization derives from the operator key / #42 allow-list, not the SaaS operator (ADR-002 boundary). Local allow-list first; operator-published (NIP-51-style) sync later.
+- **Dev bypass blast radius** — `VITE_SKIP_ACCESS_GATE` is build-time and never set in a production image; `devUnlock` is gated by `accessControl.devUnlock` (off in a locked-down deployment) and every dev unlock is audited with role `operator`/`dev`.
+
+## Resolved decisions (2026-07-29)
+
+1. **Session model** — ✅ one badge = one **transaction-scoped session**, with the `session` context modeled generally (terminal access, not a transaction handle) to allow non-transaction functions and per-action **step-up auth** (tap phone / PIN) later. See *Session semantics* above.
+2. **v1 credential** — ✅ **UID allow-list first** (hashed), behind a `CardCredential` union so challenge-response is additive (PR5).
+3. **Allow-list home** — ✅ **local first** (`state.db` / provisioned `access.json`, peer of `branding/`); operator-Nostr sync is a later PR.
+
+Still open (cosmetic, decide during PR2):
+
+4. **Dev unlock affordance** — hidden long-press corner vs a labeled button on the existing debug bar.
+
+---
+
+## Implementation plan (phased PRs)
+
+Each PR is independently mergeable. **PR1 changes nothing observable while `accessControl.enabled=false` (the default).**
+
+### PR1 — Non-breaking skeleton (state + config + mock reader + dev bypass + audit stub)
+**Goal:** the locked→idle→transaction path is exercisable on the batm3 today, and the flag-off machine is byte-for-byte behavior-identical.
+- `packages/state-machine`: add `locked` state (`initial`), `ACCESS_GRANTED`/`ACCESS_DENIED`/`DEV_UNLOCK` events, `accessBypass`/`devUnlockAllowed` guards, `startSession`/`recordAccess*` actions, context fields + actor `input`. Re-point `complete`/inactivity re-lock targets to `locked`.
+- `apps/machine/src/types/electron.d.ts`: `RuntimeConfig.accessControl`.
+- `apps/machine/electron/main.ts`: `get-config` returns `accessControl` (env-sourced); `.env.example` documents `VITE_SKIP_ACCESS_GATE` + `ACCESS_CONTROL_ENABLED`.
+- `apps/machine/src/services/access/`: `types.ts`, `mock-reader.ts`, `authorize.ts` (UID allow-list, hashed), `index.ts`.
+- `apps/machine/src/stores/atm.ts`: actor `input`, `isLocked`, `grantAccess`/`denyAccess`/`devUnlock`, reader subscription (only when enabled).
+- `apps/machine/src/views/LockedView.vue` + `App.vue` `locked` render branch.
+- Audit stub: `recordAccessEvent` handler + preload exposure (local write only).
+- **Tests:** state-machine `locked → idle` on grant; `always`-bypass when disabled; re-lock from `complete`; `authorize()` allow/deny; `devUnlock` gated by config. 
+- **Flag state on merge:** `enabled=false`. CI green = no behavior change.
+
+### PR2 — Locked UX polish
+- Reader status/animation, brand-aware LockedView, denied-flash + reason, inactivity copy, operator/dev unlock affordance per open-question #4. Pure renderer.
+
+### PR3 — Web NFC reader (dev)
+- `web-nfc-reader.ts` (`NDEFReader`), registered in `availableAccessReaders()` behind availability check. Lets a laptop/phone drive the gate for demos/dev. No hardware dependency.
+
+### PR4 — Serial NFC HAL driver (real batm3 hardware)
+- Main-process serial driver for `/dev/ttyNFC` (HAL-style per ADR-001), IPC channel `access:watch-card` + `preload.ts` exposure; `serial-reader.ts` renderer client. Requires the physical reader to validate. Document the reader's protocol/baud in `docs/device-configuration.md`.
+
+### PR5 — Challenge-response credential + operator allow-list sync
+- Extend `CardCredential` with the `challenge` variant; `authorize.ts` verifies a signature over a machine nonce against the operator-authorized set; allow-list synced from an operator-published event (#42 mechanism). This is the real security upgrade; v1 UID path stays as a fallback/dev mode.
+
+### Cross-cutting
+- **Docs:** update `docs/machine-installation.md` (enabling access control, enrolling cards) and `deploy/nixos/README.md` (the `accessControl` config + `/dev/ttyNFC`) as PR4/PR5 land.
+- **Provisioning:** a later change can add an `access.json` under `/var/lib/bitspire/` (peer of `branding/`) with the allow-list + `enabled`, plus a `provision-access.sh` mirroring `provision-branding.sh`.
diff --git a/packages/state-machine/src/__tests__/access-control.test.ts b/packages/state-machine/src/__tests__/access-control.test.ts
new file mode 100644
index 0000000..d9dff5c
--- /dev/null
+++ b/packages/state-machine/src/__tests__/access-control.test.ts
@@ -0,0 +1,83 @@
+import { describe, it, expect } from 'vitest'
+import { createActor } from 'xstate'
+import { createATMMachine } from '../machine.js'
+
+// ADR-003 access gate. Key invariant: with the gate DISABLED (the default),
+// the machine is behaviourally identical to the pre-access machine — it
+// settles into `idle` on start via the `locked` state's `always` bypass.
+describe('ATM access control (ADR-003)', () => {
+  describe('gate disabled (default)', () => {
+    it('settles into idle on start (non-breaking)', () => {
+      const actor = createActor(createATMMachine())
+      actor.start()
+      expect(actor.getSnapshot().value).toBe('idle')
+    })
+
+    it('settles into idle even with accessControlEnabled:false explicit', () => {
+      const actor = createActor(createATMMachine({}, { accessControlEnabled: false }))
+      actor.start()
+      expect(actor.getSnapshot().value).toBe('idle')
+    })
+  })
+
+  describe('gate enabled', () => {
+    it('stays locked on start', () => {
+      const actor = createActor(createATMMachine({}, { accessControlEnabled: true }))
+      actor.start()
+      expect(actor.getSnapshot().value).toBe('locked')
+      expect(actor.getSnapshot().context.accessSession).toBeNull()
+    })
+
+    it('ACCESS_GRANTED unlocks to idle and records the session', () => {
+      const actor = createActor(createATMMachine({}, { accessControlEnabled: true }))
+      actor.start()
+      actor.send({ type: 'ACCESS_GRANTED', role: 'user', credentialIdHash: 'abc123' })
+
+      const snap = actor.getSnapshot()
+      expect(snap.value).toBe('idle')
+      expect(snap.context.accessSession).toMatchObject({ role: 'user', credentialIdHash: 'abc123' })
+      expect(typeof snap.context.accessSession?.grantedAt).toBe('number')
+    })
+
+    it('ACCESS_DENIED stays locked and surfaces the reason', () => {
+      const actor = createActor(createATMMachine({}, { accessControlEnabled: true }))
+      actor.start()
+      actor.send({ type: 'ACCESS_DENIED', reason: 'card not authorized' })
+
+      const snap = actor.getSnapshot()
+      expect(snap.value).toBe('locked')
+      expect(snap.context.accessDenyReason).toBe('card not authorized')
+    })
+
+    it('DEV_UNLOCK unlocks to idle (operator session)', () => {
+      const actor = createATMMachine({}, { accessControlEnabled: true })
+      const running = createActor(actor)
+      running.start()
+      running.send({ type: 'DEV_UNLOCK' })
+
+      const snap = running.getSnapshot()
+      expect(snap.value).toBe('idle')
+      expect(snap.context.accessSession?.role).toBe('operator')
+    })
+  })
+
+  describe('build/dev bypass', () => {
+    it('accessBypassFlag opens the gate even when enabled', () => {
+      const actor = createActor(
+        createATMMachine({}, { accessControlEnabled: true, accessBypassFlag: true })
+      )
+      actor.start()
+      expect(actor.getSnapshot().value).toBe('idle')
+    })
+
+    it('DEV_UNLOCK is a no-op while bypassing (already idle)', () => {
+      const actor = createActor(
+        createATMMachine({}, { accessControlEnabled: true, accessBypassFlag: true })
+      )
+      actor.start()
+      // already idle; DEV_UNLOCK guard is false, so no throw / no change
+      actor.send({ type: 'DEV_UNLOCK' })
+      expect(actor.getSnapshot().value).toBe('idle')
+    })
+  })
+})
diff --git a/packages/state-machine/src/index.ts b/packages/state-machine/src/index.ts
index a72e082..68c793b 100644
--- a/packages/state-machine/src/index.ts
+++ b/packages/state-machine/src/index.ts
@@ -52,6 +52,8 @@ export {
   type PaymentMethod,
   type DispenseCashResult,
   type CassetteBillResult,
+  type AccessRole,
+  type AccessSession,
   initialContext,
 } from './types.js'
 
diff --git a/packages/state-machine/src/machine.ts b/packages/state-machine/src/machine.ts
index c889127..c1a97b3 100644
--- a/packages/state-machine/src/machine.ts
+++ b/packages/state-machine/src/machine.ts
@@ -22,6 +22,14 @@ export interface ATMMachineOptions {
   currency?: string
   cashInFeeFraction?: number
   cashOutFeeFraction?: number
+  /**
+   * ADR-003 access gate. When true, the machine boots into `locked` and
+   * waits for an ACCESS_GRANTED (or DEV_UNLOCK) before reaching `idle`.
+   * Defaults false → `locked` immediately bypasses to `idle` (no gate).
+   */
+  accessControlEnabled?: boolean
+  /** Build/dev bypass (VITE_SKIP_ACCESS_GATE) — opens the gate even when enabled. */
+  accessBypassFlag?: boolean
 }
 
 export function createATMMachine(
@@ -167,9 +175,41 @@ export function createATMMachine(
         inventory: context.inventory,
         cashInFeeFraction: context.cashInFeeFraction,
         cashOutFeeFraction: context.cashOutFeeFraction,
+        // Preserve the access-gate config across resets — it comes from
+        // machine options, not the transaction, and must survive re-lock.
+        accessControlEnabled: context.accessControlEnabled,
+        accessBypassFlag: context.accessBypassFlag,
+        // Preserve the active access session: `idle`'s entry runs resetContext
+        // AFTER the locked→idle transition action that set the session, so
+        // without this the just-granted session would be wiped. The session is
+        // cleared instead on re-lock (locked's entry), i.e. when access ends.
+        accessSession: context.accessSession,
         cashInSessionId: null,
         dispenseResult: null,
       })),
+      // ADR-003 access-control actions
+      startAccessSession: assign({
+        accessSession: ({ event }) => {
+          if (event.type !== 'ACCESS_GRANTED') return null
+          return { role: event.role, grantedAt: Date.now(), credentialIdHash: event.credentialIdHash }
+        },
+        accessDenyReason: null,
+      }),
+      startDevAccessSession: assign({
+        accessSession: () => ({
+          role: 'operator' as const,
+          grantedAt: Date.now(),
+          credentialIdHash: 'dev-unlock',
+        }),
+        accessDenyReason: null,
+      }),
+      setAccessDenyReason: assign({
+        accessDenyReason: ({ event }) => (event.type === 'ACCESS_DENIED' ? event.reason : null),
+      }),
+      clearAccessDenyReason: assign({ accessDenyReason: null }),
+      // On (re-)entering `locked`, access has ended: drop any prior session so a
+      // stale grant can't leak across the gate.
+      clearAccessSession: assign({ accessSession: null }),
       setStartTime: assign({
         startedAt: () => Date.now(),
         txid: () => generateTxId(),
@@ -376,6 +416,12 @@ export function createATMMachine(
       }),
     },
     guards: {
+      // ADR-003: gate is open when access control is off, or the build/dev
+      // bypass is set. Used by `locked`'s eventless `always` transition so a
+      // machine with the gate disabled settles straight into `idle`.
+      accessBypass: ({ context }) => !context.accessControlEnabled || context.accessBypassFlag,
+      // The dev unlock is only meaningful when the gate is actually engaged.
+      devUnlockAllowed: ({ context }) => context.accessControlEnabled && !context.accessBypassFlag,
       hasInsertedBills: ({ context }) => context.billsInserted.length > 0,
       // Legacy brain.js parity: "send coins" is a no-op while a bill is
       // between the stack command and the validator's stacked-confirmation.
@@ -429,7 +475,10 @@ export function createATMMachine(
     },
   }).createMachine({
     id: 'atm',
-    initial: 'idle',
+    // ADR-003: `locked` is the resting state. With the gate disabled (the
+    // default), its `always` transition bypasses straight to `idle` on start,
+    // so behavior is identical to the pre-access machine.
+    initial: 'locked',
     context: {
       ...initialContext,
       ...(options?.currency ? { currency: options.currency } : {}),
@@ -437,6 +486,12 @@ export function createATMMachine(
       ...(options?.cashOutFeeFraction !== undefined
         ? { cashOutFeeFraction: options.cashOutFeeFraction }
         : {}),
+      ...(options?.accessControlEnabled !== undefined
+        ? { accessControlEnabled: options.accessControlEnabled }
+        : {}),
+      ...(options?.accessBypassFlag !== undefined
+        ? { accessBypassFlag: options.accessBypassFlag }
+        : {}),
     },
     // Root-level handler: lets the operator-fees subscriber update the
     // active fee fractions reactively. Next cashIn/cashOut entry will
@@ -451,6 +506,22 @@ export function createATMMachine(
       },
     },
     states: {
+      // === ACCESS GATE (ADR-003) ===
+      // Resting/locked state. A paired, healthy machine sits here until a
+      // valid credential is presented. When the gate is disabled (default)
+      // the eventless `always` transition immediately hands off to `idle`,
+      // so a non-access machine never dwells here.
+      locked: {
+        entry: ['clearAccessDenyReason', 'clearAccessSession'],
+        always: [{ guard: 'accessBypass', target: 'idle' }],
+        on: {
+          ACCESS_GRANTED: { target: 'idle', actions: 'startAccessSession' },
+          DEV_UNLOCK: { guard: 'devUnlockAllowed', target: 'idle', actions: 'startDevAccessSession' },
+          // A denied tap keeps us locked; record the reason for the screen.
+          ACCESS_DENIED: { actions: 'setAccessDenyReason' },
+        },
+      },
+
       idle: {
         entry: 'resetContext',
         on: {
@@ -491,7 +562,7 @@ export function createATMMachine(
               INACTIVITY_TIMEOUT: [
                 {
                   guard: ({ context }) => context.billsInserted.length === 0,
-                  target: '#atm.idle',
+                  target: '#atm.locked',
                 },
                 {
                   target: 'confirmAbandon',
@@ -524,7 +595,7 @@ export function createATMMachine(
                 {
                   // No bills inserted yet: safe to cancel
                   guard: ({ context }) => context.billsInserted.length === 0,
-                  target: '#atm.idle',
+                  target: '#atm.locked',
                 },
                 {
                   // Bills already stacked: warn user before abandoning
@@ -534,7 +605,7 @@ export function createATMMachine(
               TIMEOUT: [
                 {
                   guard: ({ context }) => context.billsInserted.length === 0,
-                  target: '#atm.idle',
+                  target: '#atm.locked',
                 },
                 {
                   target: 'confirmAbandon',
@@ -586,10 +657,10 @@ export function createATMMachine(
             // like the rest — clear the marker so nothing blocks on it.
             entry: 'clearBillPending',
             after: {
-              60000: '#atm.idle',
+              60000: '#atm.locked',
             },
             on: {
-              CANCEL: '#atm.idle', // User confirms they want to leave
+              CANCEL: '#atm.locked', // User confirms they want to leave
               RETRY: 'generatingNdebit', // Go back and try again
             },
           },
@@ -614,10 +685,10 @@ export function createATMMachine(
           },
           complete: {
             after: {
-              COMPLETE_DELAY: '#atm.idle',
+              COMPLETE_DELAY: '#atm.locked',
             },
             on: {
-              CANCEL: '#atm.idle',
+              CANCEL: '#atm.locked',
             },
           },
           error: {
@@ -646,7 +717,7 @@ export function createATMMachine(
                 {
                   // No bills inserted: safe to cancel
                   guard: ({ context }) => context.billsInserted.length === 0,
-                  target: '#atm.idle',
+                  target: '#atm.locked',
                 },
                 {
                   // Bills inserted: show abandon warning first
@@ -689,7 +760,7 @@ export function createATMMachine(
             // User selects denomination buttons to build up the cash amount
             // UI shows: available denominations, running total, sats equivalent
             after: {
-              INACTIVITY_TIMEOUT: '#atm.idle',
+              INACTIVITY_TIMEOUT: '#atm.locked',
             },
             entry: 'clearCashOutSelection',
             on: {
@@ -709,8 +780,8 @@ export function createATMMachine(
                 target: 'generatingInvoice',
                 actions: 'calculateDispenseFromSelection',
               },
-              CANCEL: '#atm.idle',
-              TIMEOUT: '#atm.idle',
+              CANCEL: '#atm.locked',
+              TIMEOUT: '#atm.locked',
             },
           },
           generatingInvoice: {
@@ -758,7 +829,7 @@ export function createATMMachine(
               TIMEOUT: {
                 target: 'selectingAmount',
               },
-              CANCEL: '#atm.idle',
+              CANCEL: '#atm.locked',
             },
           },
           dispensingCash: {
@@ -826,20 +897,20 @@ export function createATMMachine(
           },
           complete: {
             after: {
-              COMPLETE_DELAY: '#atm.idle',
+              COMPLETE_DELAY: '#atm.locked',
             },
             on: {
-              CANCEL: '#atm.idle',
+              CANCEL: '#atm.locked',
             },
           },
           dispenseError: {
             // Payment received but cash not (fully) dispensed.
             // Show error + txid for 30s, then auto-idle (matches brain.js _timedState).
             after: {
-              DISPENSE_ERROR_TIMEOUT: '#atm.idle',
+              DISPENSE_ERROR_TIMEOUT: '#atm.locked',
             },
             on: {
-              CANCEL: '#atm.idle',
+              CANCEL: '#atm.locked',
             },
           },
           error: {
@@ -849,7 +920,7 @@ export function createATMMachine(
                 target: 'fetchingRate',
                 actions: 'incrementRetry',
               },
-              CANCEL: '#atm.idle',
+              CANCEL: '#atm.locked',
             },
           },
         },
diff --git a/packages/state-machine/src/types.ts b/packages/state-machine/src/types.ts
index 3a2810e..9556004 100644
--- a/packages/state-machine/src/types.ts
+++ b/packages/state-machine/src/types.ts
@@ -48,8 +48,47 @@ export interface OfferRequestEvent {
   description?: string
 }
 
+/**
+ * Access-control role resolved from a presented credential.
+ * `user` may transact; `operator` may additionally reach operator
+ * functions (config/maintenance/enrollment) — reserved for later PRs.
+ * See ADR-003.
+ */
+export type AccessRole = 'user' | 'operator'
+
+/**
+ * An active access session, created when a valid credential is presented
+ * (or via the dev unlock). Modeled as general *terminal access*, not a
+ * transaction handle, so the terminal can later gate non-transaction
+ * functions and per-action step-up auth (ADR-003).
+ */
+export interface AccessSession {
+  role: AccessRole
+  /** ms epoch when access was granted */
+  grantedAt: number
+  /** salted hash of the presented credential id — never the raw UID (KYC-free) */
+  credentialIdHash: string
+}
+
 /** ATM machine context */
 export interface ATMContext {
+  // Access control (ADR-003)
+  /**
+   * Whether the badge-to-enter access gate is active. When false (the
+   * default), the machine's `locked` initial state immediately bypasses
+   * to `idle` — behavior is identical to a machine with no access layer.
+   */
+  accessControlEnabled: boolean
+  /**
+   * Build/dev bypass (VITE_SKIP_ACCESS_GATE). Forces the gate open even
+   * when accessControlEnabled is true — for browser dev / CI.
+   */
+  accessBypassFlag: boolean
+  /** Active access session, or null while locked. */
+  accessSession: AccessSession | null
+  /** Reason for the last denied access attempt (for the locked screen). */
+  accessDenyReason: string | null
+
   // Transaction details
   /** Fiat amount in cents */
   fiatCents: number
@@ -136,6 +175,10 @@ export type ATMEvent =
   | { type: 'SELECT_CASH_IN' }
   | { type: 'SELECT_CASH_OUT' }
   | { type: 'CANCEL' }
+  // Access control (ADR-003)
+  | { type: 'ACCESS_GRANTED'; role: AccessRole; credentialIdHash: string }
+  | { type: 'ACCESS_DENIED'; reason: string }
+  | { type: 'DEV_UNLOCK' }
   | { type: 'SELECT_AMOUNT'; amount: number }
   | { type: 'FINISH_INSERTING' }
   | { type: 'USER_SCANNED_NPUB'; npub: string }
@@ -173,6 +216,12 @@ export type ATMEvent =
 
 /** Initial context values */
 export const initialContext: ATMContext = {
+  // Access control defaults OFF — a machine built without the access
+  // options behaves exactly as before (locked → bypass → idle). See ADR-003.
+  accessControlEnabled: false,
+  accessBypassFlag: false,
+  accessSession: null,
+  accessDenyReason: null,
   fiatCents: 0,
   satsAmount: 0,
   currency: 'USD',