diff --git a/apps/desktop/src/components/AppShell.tsx b/apps/desktop/src/components/AppShell.tsx
index 47d2fd0..fc6396f 100644
--- a/apps/desktop/src/components/AppShell.tsx
+++ b/apps/desktop/src/components/AppShell.tsx
@@ -2,6 +2,7 @@ import { useEffect } from 'react';
 import { Outlet } from 'react-router-dom';
 
 import { useAuth } from '../context/AuthContext';
+import { useIdleAutoLock } from '../hooks/useIdleAutoLock';
 import { startConversationKeySync } from '../lib/conversationKeySync';
 import { startDeviceApprovalListener } from '../lib/deviceApproval';
 import { ensureInstallId } from '../lib/installId';
@@ -14,6 +15,7 @@ import { Sidebar } from './Sidebar';
 
 export function AppShell() {
   const { session } = useAuth();
+  useIdleAutoLock();
   useMentionNotifications(session?.user.id);
   useEffect(() => {
     // Prompt once per authenticated shell mount. Module-level guard prevents
diff --git a/apps/desktop/src/components/SecurityCenter.tsx b/apps/desktop/src/components/SecurityCenter.tsx
index 1be195a..8f02551 100644
--- a/apps/desktop/src/components/SecurityCenter.tsx
+++ b/apps/desktop/src/components/SecurityCenter.tsx
@@ -1,5 +1,11 @@
 import { useState } from 'react';
 
+import {
+  type AutoLockMinutes,
+  getAutoLockMinutes,
+  notifyAutoLockChanged,
+  setAutoLockMinutes,
+} from '../lib/autoLockSettings';
 import { isWipeOnCloseEnabled, setWipeOnClose } from '../lib/memoryWipeSettings';
 import {
   changePin,
@@ -21,6 +27,7 @@ export function SecurityCenter({ userId }: Props) {
   const [recovery, setRecovery] = useState<string | null>(null);
   const [migration, setMigration] = useState<LegacyMigrationReport | null>(null);
   const [wipeOnClose, setWipeOnCloseState] = useState<boolean>(() => isWipeOnCloseEnabled());
+  const [autoLockMinutes, setAutoLockMinutesState] = useState<AutoLockMinutes>(() => getAutoLockMinutes());
 
   async function handleRetryMigration() {
     setBusy(true); setMsg(null); setMigration(null);
@@ -149,6 +156,39 @@ export function SecurityCenter({ userId }: Props) {
         </label>
       </section>
 
+      <section>
+        <h3 className="mb-2 text-xs font-medium uppercase tracking-wide text-fg-muted">
+          Auto-Lock nach Inaktivität
+        </h3>
+        <p className="mb-2 text-xs text-fg-muted">
+          Verlangt erneute PIN-Eingabe nach der gewählten Inaktivitätsdauer. Empfohlen für gemeinsam genutzte Rechner.
+        </p>
+        <div className="flex items-center justify-between gap-3">
+          <div>
+            <div className="text-sm font-medium text-fg">Automatisch sperren</div>
+            <div className="text-xs text-fg-muted">
+              Verlangt erneute PIN-Eingabe nach X Minuten Inaktivität.
+            </div>
+          </div>
+          <select
+            value={autoLockMinutes}
+            onChange={(e) => {
+              const next = Number(e.target.value) as AutoLockMinutes;
+              setAutoLockMinutes(next);
+              notifyAutoLockChanged(next);
+              setAutoLockMinutesState(next);
+            }}
+            className="cursor-pointer rounded-md border border-line bg-surface-2 px-3 py-1.5 text-sm text-fg focus:border-accent focus:outline-none focus:ring-1 focus:ring-accent/40"
+          >
+            <option value={0}>Aus</option>
+            <option value={5}>5 min</option>
+            <option value={15}>15 min</option>
+            <option value={30}>30 min</option>
+            <option value={60}>60 min</option>
+          </select>
+        </div>
+      </section>
+
       <section>
         <h3 className="mb-2 text-xs font-medium uppercase tracking-wide text-rose-400">Identität zurücksetzen</h3>
         <p className="mb-2 text-xs text-fg-muted">Erstellt einen neuen Schlüssel. Alle alten Chats werden unlesbar.</p>
diff --git a/apps/desktop/src/hooks/useIdleAutoLock.ts b/apps/desktop/src/hooks/useIdleAutoLock.ts
new file mode 100644
index 0000000..fd8bb5b
--- /dev/null
+++ b/apps/desktop/src/hooks/useIdleAutoLock.ts
@@ -0,0 +1,79 @@
+import { useEffect, useRef } from 'react';
+
+import { useAuth } from '../context/AuthContext';
+import {
+  getAutoLockMinutes,
+  subscribeAutoLockSetting,
+  type AutoLockMinutes,
+} from '../lib/autoLockSettings';
+
+const ACTIVITY_EVENTS: Array<keyof WindowEventMap> = [
+  'keydown',
+  'mousedown',
+  'pointermove',
+  'touchstart',
+  'wheel',
+];
+
+// Throttle activity-event resets to once per second to avoid thrashing the
+// timer on rapid mouse movement.
+const RESET_THROTTLE_MS = 1000;
+
+export function useIdleAutoLock(): void {
+  const { session, signOut } = useAuth();
+  const minutesRef = useRef<AutoLockMinutes>(getAutoLockMinutes());
+  const timerRef = useRef<number | null>(null);
+  const lastResetAtRef = useRef<number>(0);
+
+  // Keep minutesRef live to the setting.
+  useEffect(() => {
+    const unsub = subscribeAutoLockSetting((v) => {
+      minutesRef.current = v;
+      scheduleNext();
+    });
+    return unsub;
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, []);
+
+  // Helper: schedule the lock based on the current setting.
+  function scheduleNext(): void {
+    if (timerRef.current !== null) {
+      window.clearTimeout(timerRef.current);
+      timerRef.current = null;
+    }
+    const min = minutesRef.current;
+    if (min === 0) return; // disabled
+    timerRef.current = window.setTimeout(() => {
+      timerRef.current = null;
+      // Fire the lock. signOut wipes local state and navigates to /device
+      // (PIN re-entry screen).
+      void signOut().catch((err) => console.warn('auto-lock signOut failed', err));
+    }, min * 60 * 1000);
+  }
+
+  useEffect(() => {
+    if (!session) return;
+    scheduleNext();
+
+    const onActivity = () => {
+      const now = Date.now();
+      if (now - lastResetAtRef.current < RESET_THROTTLE_MS) return;
+      lastResetAtRef.current = now;
+      scheduleNext();
+    };
+
+    for (const ev of ACTIVITY_EVENTS) {
+      window.addEventListener(ev, onActivity, { passive: true });
+    }
+    return () => {
+      for (const ev of ACTIVITY_EVENTS) {
+        window.removeEventListener(ev, onActivity);
+      }
+      if (timerRef.current !== null) {
+        window.clearTimeout(timerRef.current);
+        timerRef.current = null;
+      }
+    };
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [session]);
+}
diff --git a/apps/desktop/src/lib/autoLockSettings.ts b/apps/desktop/src/lib/autoLockSettings.ts
new file mode 100644
index 0000000..3b2ba17
--- /dev/null
+++ b/apps/desktop/src/lib/autoLockSettings.ts
@@ -0,0 +1,43 @@
+// Per-install setting for PIN-idle-auto-lock. 0 = disabled.
+// Values match the dropdown options (5/15/30/60 minutes).
+
+const KEY = 'chatapp.autoLockMinutes.v1';
+
+export type AutoLockMinutes = 0 | 5 | 15 | 30 | 60;
+
+const VALID: AutoLockMinutes[] = [0, 5, 15, 30, 60];
+
+export function getAutoLockMinutes(): AutoLockMinutes {
+  try {
+    const raw = window.localStorage.getItem(KEY);
+    if (!raw) return 0;
+    const n = Number(raw);
+    if (VALID.includes(n as AutoLockMinutes)) return n as AutoLockMinutes;
+    return 0;
+  } catch {
+    return 0;
+  }
+}
+
+type Listener = (value: AutoLockMinutes) => void;
+const listeners = new Set<Listener>();
+
+export function subscribeAutoLockSetting(l: Listener): () => void {
+  listeners.add(l);
+  return () => listeners.delete(l);
+}
+
+export function notifyAutoLockChanged(value: AutoLockMinutes): void {
+  for (const l of listeners) {
+    try { l(value); } catch (err) { console.warn(err); }
+  }
+}
+
+export function setAutoLockMinutes(value: AutoLockMinutes): void {
+  try {
+    window.localStorage.setItem(KEY, String(value));
+  } catch {
+    /* quota */
+  }
+  notifyAutoLockChanged(value);
+}
diff --git a/apps/desktop/src/lib/memoryWipe.ts b/apps/desktop/src/lib/memoryWipe.ts
index a469a2b..47363df 100644
--- a/apps/desktop/src/lib/memoryWipe.ts
+++ b/apps/desktop/src/lib/memoryWipe.ts
@@ -16,6 +16,7 @@ const PRESERVE_LOCAL_STORAGE = new Set([
   'chatapp.locale',
   'chatapp.installId',
   'chatapp.wipeOnClose.v1',
+  'chatapp.autoLockMinutes.v1',
   'i18nextLng',
 ]);