diff --git a/backend/alembic/versions/025_add_auto_lock_settings.py b/backend/alembic/versions/025_add_auto_lock_settings.py
new file mode 100644
index 0000000..a50992c
--- /dev/null
+++ b/backend/alembic/versions/025_add_auto_lock_settings.py
@@ -0,0 +1,30 @@
+"""Add auto-lock settings columns to settings table.
+
+Revision ID: 025
+Revises: 024
+Create Date: 2026-02-25
+"""
+from alembic import op
+import sqlalchemy as sa
+
+# revision identifiers
+revision = "025"
+down_revision = "024"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "settings",
+        sa.Column("auto_lock_enabled", sa.Boolean(), server_default="false", nullable=False),
+    )
+    op.add_column(
+        "settings",
+        sa.Column("auto_lock_minutes", sa.Integer(), server_default="5", nullable=False),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("settings", "auto_lock_minutes")
+    op.drop_column("settings", "auto_lock_enabled")
diff --git a/backend/app/models/settings.py b/backend/app/models/settings.py
index 6552d7c..cf5ea87 100644
--- a/backend/app/models/settings.py
+++ b/backend/app/models/settings.py
@@ -42,6 +42,10 @@ class Settings(Base):
     ntfy_todo_lead_days: Mapped[int] = mapped_column(Integer, default=1, server_default="1")
     ntfy_project_lead_days: Mapped[int] = mapped_column(Integer, default=2, server_default="2")
 
+    # Auto-lock settings
+    auto_lock_enabled: Mapped[bool] = mapped_column(Boolean, default=False, server_default="false")
+    auto_lock_minutes: Mapped[int] = mapped_column(Integer, default=5, server_default="5")
+
     @property
     def ntfy_has_token(self) -> bool:
         """Derived field for SettingsResponse — True when an auth token is stored."""
diff --git a/backend/app/routers/auth.py b/backend/app/routers/auth.py
index 854e5bf..8515fa6 100644
--- a/backend/app/routers/auth.py
+++ b/backend/app/routers/auth.py
@@ -28,7 +28,7 @@ from app.database import get_db
 from app.models.user import User
 from app.models.session import UserSession
 from app.models.settings import Settings
-from app.schemas.auth import SetupRequest, LoginRequest, ChangePasswordRequest
+from app.schemas.auth import SetupRequest, LoginRequest, ChangePasswordRequest, VerifyPasswordRequest
 from app.services.auth import (
     hash_password,
     verify_password_with_upgrade,
@@ -373,6 +373,29 @@ async def auth_status(
     return {"authenticated": authenticated, "setup_required": setup_required}
 
 
+@router.post("/verify-password")
+async def verify_password(
+    data: VerifyPasswordRequest,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """
+    Verify the current user's password without changing anything.
+    Used by the frontend lock screen to re-authenticate without a full login.
+    Also handles transparent bcrypt→Argon2id upgrade.
+    """
+    valid, new_hash = verify_password_with_upgrade(data.password, current_user.password_hash)
+    if not valid:
+        raise HTTPException(status_code=401, detail="Invalid password")
+
+    # Persist upgraded hash if migration happened
+    if new_hash:
+        current_user.password_hash = new_hash
+        await db.commit()
+
+    return {"verified": True}
+
+
 @router.post("/change-password")
 async def change_password(
     data: ChangePasswordRequest,
diff --git a/backend/app/routers/settings.py b/backend/app/routers/settings.py
index 50d0959..6ac79a3 100644
--- a/backend/app/routers/settings.py
+++ b/backend/app/routers/settings.py
@@ -36,6 +36,8 @@ def _to_settings_response(s: Settings) -> SettingsResponse:
         ntfy_todo_lead_days=s.ntfy_todo_lead_days,
         ntfy_project_lead_days=s.ntfy_project_lead_days,
         ntfy_has_token=bool(s.ntfy_auth_token),  # derived — never expose the token value
+        auto_lock_enabled=s.auto_lock_enabled,
+        auto_lock_minutes=s.auto_lock_minutes,
         created_at=s.created_at,
         updated_at=s.updated_at,
     )
diff --git a/backend/app/schemas/auth.py b/backend/app/schemas/auth.py
index eb09b0d..198eb89 100644
--- a/backend/app/schemas/auth.py
+++ b/backend/app/schemas/auth.py
@@ -60,3 +60,7 @@ class ChangePasswordRequest(BaseModel):
     @classmethod
     def validate_new_password(cls, v: str) -> str:
         return _validate_password_strength(v)
+
+
+class VerifyPasswordRequest(BaseModel):
+    password: str
diff --git a/backend/app/schemas/settings.py b/backend/app/schemas/settings.py
index ab32bee..8591e62 100644
--- a/backend/app/schemas/settings.py
+++ b/backend/app/schemas/settings.py
@@ -31,6 +31,17 @@ class SettingsUpdate(BaseModel):
     ntfy_todo_lead_days: Optional[int] = None
     ntfy_project_lead_days: Optional[int] = None
 
+    # Auto-lock settings
+    auto_lock_enabled: Optional[bool] = None
+    auto_lock_minutes: Optional[int] = None
+
+    @field_validator('auto_lock_minutes')
+    @classmethod
+    def validate_auto_lock_minutes(cls, v: Optional[int]) -> Optional[int]:
+        if v is not None and not (1 <= v <= 60):
+            raise ValueError("auto_lock_minutes must be between 1 and 60")
+        return v
+
     @field_validator('first_day_of_week')
     @classmethod
     def validate_first_day(cls, v: int | None) -> int | None:
@@ -134,6 +145,10 @@ class SettingsResponse(BaseModel):
     # Derived field: computed via Settings.ntfy_has_token property (from_attributes reads it)
     ntfy_has_token: bool = False
 
+    # Auto-lock settings
+    auto_lock_enabled: bool = False
+    auto_lock_minutes: int = 5
+
     created_at: datetime
     updated_at: datetime
 
diff --git a/frontend/src/components/auth/AmbientBackground.tsx b/frontend/src/components/auth/AmbientBackground.tsx
new file mode 100644
index 0000000..d169c80
--- /dev/null
+++ b/frontend/src/components/auth/AmbientBackground.tsx
@@ -0,0 +1,45 @@
+/**
+ * Shared animated ambient background for the login screen and lock overlay.
+ * Renders floating gradient orbs and a subtle grid overlay.
+ */
+export default function AmbientBackground() {
+  return (
+    <div className="pointer-events-none absolute inset-0 overflow-hidden" aria-hidden="true">
+      {/* Animated gradient orbs */}
+      <div
+        className="absolute h-[500px] w-[500px] rounded-full opacity-15 blur-[100px] animate-drift-1"
+        style={{
+          background: 'radial-gradient(circle, hsl(var(--accent-color)) 0%, transparent 70%)',
+          top: '-10%',
+          left: '-10%',
+        }}
+      />
+      <div
+        className="absolute h-[400px] w-[400px] rounded-full opacity-10 blur-[100px] animate-drift-2"
+        style={{
+          background: 'radial-gradient(circle, hsl(var(--accent-color)) 0%, transparent 70%)',
+          bottom: '-5%',
+          right: '-5%',
+        }}
+      />
+      <div
+        className="absolute h-[350px] w-[350px] rounded-full opacity-[0.07] blur-[80px] animate-drift-3"
+        style={{
+          background: 'radial-gradient(circle, hsl(var(--accent-color)) 0%, transparent 70%)',
+          top: '40%',
+          right: '20%',
+        }}
+      />
+
+      {/* Subtle grid overlay */}
+      <div
+        className="absolute inset-0 opacity-[0.035]"
+        style={{
+          backgroundImage:
+            'linear-gradient(rgba(255,255,255,0.5) 1px, transparent 1px), linear-gradient(90deg, rgba(255,255,255,0.5) 1px, transparent 1px)',
+          backgroundSize: '60px 60px',
+        }}
+      />
+    </div>
+  );
+}
diff --git a/frontend/src/components/auth/LockScreen.tsx b/frontend/src/components/auth/LockScreen.tsx
index 57895bd..7320f3a 100644
--- a/frontend/src/components/auth/LockScreen.tsx
+++ b/frontend/src/components/auth/LockScreen.tsx
@@ -9,6 +9,7 @@ import { Input } from '@/components/ui/input';
 import { Button } from '@/components/ui/button';
 import { Label } from '@/components/ui/label';
 import { cn } from '@/lib/utils';
+import AmbientBackground from './AmbientBackground';
 
 /** Validates password against backend rules: 12-128 chars, at least one letter + one non-letter. */
 function validatePassword(password: string): string | null {
@@ -92,20 +93,10 @@ export default function LockScreen() {
 
   return (
     <div className="relative flex min-h-screen flex-col items-center justify-center bg-background p-4 overflow-hidden">
-      {/* Ambient glow blobs */}
-      <div className="pointer-events-none absolute inset-0" aria-hidden="true">
-        <div
-          className="absolute -top-32 -left-32 h-96 w-96 rounded-full opacity-20 blur-3xl"
-          style={{ background: 'radial-gradient(circle, hsl(var(--accent-color)) 0%, transparent 70%)' }}
-        />
-        <div
-          className="absolute -bottom-32 -right-32 h-96 w-96 rounded-full opacity-10 blur-3xl"
-          style={{ background: 'radial-gradient(circle, hsl(var(--accent-color)) 0%, transparent 70%)' }}
-        />
-      </div>
+      <AmbientBackground />
 
       {/* Wordmark — in flex flow above card */}
-      <span className="font-heading text-2xl font-bold tracking-tight text-accent mb-6 relative z-10">
+      <span className="font-heading text-5xl sm:text-6xl font-bold tracking-tight text-accent mb-10 relative z-10 animate-slide-up">
         UMBRA
       </span>
 
diff --git a/frontend/src/components/layout/AppLayout.tsx b/frontend/src/components/layout/AppLayout.tsx
index 4b9df6a..c300cac 100644
--- a/frontend/src/components/layout/AppLayout.tsx
+++ b/frontend/src/components/layout/AppLayout.tsx
@@ -3,8 +3,10 @@ import { Outlet } from 'react-router-dom';
 import { Menu } from 'lucide-react';
 import { useTheme } from '@/hooks/useTheme';
 import { AlertsProvider } from '@/hooks/useAlerts';
+import { LockProvider } from '@/hooks/useLock';
 import { Button } from '@/components/ui/button';
 import Sidebar from './Sidebar';
+import LockOverlay from './LockOverlay';
 
 export default function AppLayout() {
   useTheme();
@@ -13,26 +15,29 @@ export default function AppLayout() {
 
   return (
     <AlertsProvider>
-      <div className="flex h-screen overflow-hidden bg-background">
-        <Sidebar
-          collapsed={collapsed}
-          onToggle={() => setCollapsed(!collapsed)}
-          mobileOpen={mobileOpen}
-          onMobileClose={() => setMobileOpen(false)}
-        />
-        <div className="flex-1 flex flex-col overflow-hidden">
-          {/* Mobile header */}
-          <div className="flex md:hidden items-center h-14 border-b bg-card px-4">
-            <Button variant="ghost" size="icon" onClick={() => setMobileOpen(true)}>
-              <Menu className="h-5 w-5" />
-            </Button>
-            <h1 className="text-lg font-bold text-accent ml-3">UMBRA</h1>
+      <LockProvider>
+        <div className="flex h-screen overflow-hidden bg-background">
+          <Sidebar
+            collapsed={collapsed}
+            onToggle={() => setCollapsed(!collapsed)}
+            mobileOpen={mobileOpen}
+            onMobileClose={() => setMobileOpen(false)}
+          />
+          <div className="flex-1 flex flex-col overflow-hidden">
+            {/* Mobile header */}
+            <div className="flex md:hidden items-center h-14 border-b bg-card px-4">
+              <Button variant="ghost" size="icon" onClick={() => setMobileOpen(true)}>
+                <Menu className="h-5 w-5" />
+              </Button>
+              <h1 className="text-lg font-bold text-accent ml-3">UMBRA</h1>
+            </div>
+            <main className="flex-1 overflow-y-auto">
+              <Outlet />
+            </main>
           </div>
-          <main className="flex-1 overflow-y-auto">
-            <Outlet />
-          </main>
         </div>
-      </div>
+        <LockOverlay />
+      </LockProvider>
     </AlertsProvider>
   );
 }
diff --git a/frontend/src/components/layout/LockOverlay.tsx b/frontend/src/components/layout/LockOverlay.tsx
new file mode 100644
index 0000000..cec2cd6
--- /dev/null
+++ b/frontend/src/components/layout/LockOverlay.tsx
@@ -0,0 +1,112 @@
+import { useState, FormEvent, useEffect, useRef } from 'react';
+import { useNavigate } from 'react-router-dom';
+import { toast } from 'sonner';
+import { Lock, Loader2 } from 'lucide-react';
+import { useLock } from '@/hooks/useLock';
+import { useAuth } from '@/hooks/useAuth';
+import { useSettings } from '@/hooks/useSettings';
+import { getErrorMessage } from '@/lib/api';
+import { Input } from '@/components/ui/input';
+import { Button } from '@/components/ui/button';
+import AmbientBackground from '@/components/auth/AmbientBackground';
+
+export default function LockOverlay() {
+  const { isLocked, unlock } = useLock();
+  const { logout } = useAuth();
+  const { settings } = useSettings();
+  const navigate = useNavigate();
+
+  const [password, setPassword] = useState('');
+  const [isUnlocking, setIsUnlocking] = useState(false);
+  const inputRef = useRef<HTMLInputElement>(null);
+
+  // Focus password input when lock activates
+  useEffect(() => {
+    if (isLocked) {
+      setPassword('');
+      // Small delay to let the overlay render
+      const t = setTimeout(() => inputRef.current?.focus(), 100);
+      return () => clearTimeout(t);
+    }
+  }, [isLocked]);
+
+  if (!isLocked) return null;
+
+  const preferredName = settings?.preferred_name;
+
+  const handleUnlock = async (e: FormEvent) => {
+    e.preventDefault();
+    if (!password.trim()) return;
+
+    setIsUnlocking(true);
+    try {
+      await unlock(password);
+    } catch (error) {
+      toast.error(getErrorMessage(error, 'Invalid password'));
+      setPassword('');
+      inputRef.current?.focus();
+    } finally {
+      setIsUnlocking(false);
+    }
+  };
+
+  const handleSwitchAccount = async () => {
+    await logout();
+    navigate('/login');
+  };
+
+  return (
+    <div className="fixed inset-0 z-50 flex flex-col items-center justify-center bg-background animate-fade-in">
+      <AmbientBackground />
+
+      <div className="relative z-10 flex flex-col items-center gap-6 w-full max-w-sm px-4 animate-slide-up">
+        {/* Lock icon */}
+        <div className="p-3 rounded-full bg-accent/10 border border-accent/20">
+          <Lock className="h-6 w-6 text-accent" />
+        </div>
+
+        {/* Greeting */}
+        <div className="text-center space-y-1">
+          <h1 className="text-2xl font-heading font-semibold text-foreground">Locked</h1>
+          {preferredName && (
+            <p className="text-sm text-muted-foreground">
+              Welcome back, {preferredName}
+            </p>
+          )}
+        </div>
+
+        {/* Password form */}
+        <form onSubmit={handleUnlock} className="w-full space-y-4">
+          <Input
+            ref={inputRef}
+            type="password"
+            value={password}
+            onChange={(e) => setPassword(e.target.value)}
+            placeholder="Enter password to unlock"
+            autoComplete="current-password"
+            className="text-center"
+          />
+          <Button type="submit" className="w-full" disabled={isUnlocking}>
+            {isUnlocking ? (
+              <>
+                <Loader2 className="h-4 w-4 animate-spin" />
+                Unlocking
+              </>
+            ) : (
+              'Unlock'
+            )}
+          </Button>
+        </form>
+
+        {/* Switch account link */}
+        <button
+          type="button"
+          onClick={handleSwitchAccount}
+          className="text-xs text-muted-foreground hover:text-foreground transition-colors"
+        >
+          Switch account
+        </button>
+      </div>
+    </div>
+  );
+}
diff --git a/frontend/src/components/layout/Sidebar.tsx b/frontend/src/components/layout/Sidebar.tsx
index 9589d67..50d0e51 100644
--- a/frontend/src/components/layout/Sidebar.tsx
+++ b/frontend/src/components/layout/Sidebar.tsx
@@ -15,9 +15,11 @@ import {
   ChevronDown,
   X,
   LogOut,
+  Lock,
 } from 'lucide-react';
 import { cn } from '@/lib/utils';
 import { useAuth } from '@/hooks/useAuth';
+import { useLock } from '@/hooks/useLock';
 import { Button } from '@/components/ui/button';
 import api from '@/lib/api';
 import type { Project } from '@/types';
@@ -42,6 +44,7 @@ export default function Sidebar({ collapsed, onToggle, mobileOpen, onMobileClose
   const navigate = useNavigate();
   const location = useLocation();
   const { logout } = useAuth();
+  const { lock } = useLock();
   const [projectsExpanded, setProjectsExpanded] = useState(false);
 
   const { data: trackedProjects } = useQuery({
@@ -180,6 +183,13 @@ export default function Sidebar({ collapsed, onToggle, mobileOpen, onMobileClose
       </nav>
 
       <div className="border-t p-2 space-y-1">
+        <button
+          onClick={lock}
+          className="flex w-full items-center gap-3 rounded-lg px-3 py-2 text-sm font-medium text-muted-foreground transition-colors hover:bg-accent/10 hover:text-accent border-l-2 border-transparent"
+        >
+          <Lock className="h-5 w-5 shrink-0" />
+          {showExpanded && <span>Lock</span>}
+        </button>
         <NavLink
           to="/settings"
           onClick={mobileOpen ? onMobileClose : undefined}
diff --git a/frontend/src/components/settings/SettingsPage.tsx b/frontend/src/components/settings/SettingsPage.tsx
index 6cfbe4e..82c7e72 100644
--- a/frontend/src/components/settings/SettingsPage.tsx
+++ b/frontend/src/components/settings/SettingsPage.tsx
@@ -12,6 +12,7 @@ import {
   X,
   Search,
   Loader2,
+  Shield,
 } from 'lucide-react';
 import { useSettings } from '@/hooks/useSettings';
 import { Card, CardContent, CardDescription, CardHeader, CardTitle } from '@/components/ui/card';
@@ -20,6 +21,7 @@ import { Label } from '@/components/ui/label';
 import { cn } from '@/lib/utils';
 import api from '@/lib/api';
 import type { GeoLocation } from '@/types';
+import { Switch } from '@/components/ui/switch';
 import TotpSetupSection from './TotpSetupSection';
 import NtfySettingsSection from './NtfySettingsSection';
 
@@ -48,6 +50,8 @@ export default function SettingsPage() {
   const searchRef = useRef<HTMLDivElement>(null);
   const debounceRef = useRef<ReturnType<typeof setTimeout>>();
   const [firstDayOfWeek, setFirstDayOfWeek] = useState(settings?.first_day_of_week ?? 0);
+  const [autoLockEnabled, setAutoLockEnabled] = useState(settings?.auto_lock_enabled ?? false);
+  const [autoLockMinutes, setAutoLockMinutes] = useState(settings?.auto_lock_minutes ?? 5);
 
   // Sync state when settings load
   useEffect(() => {
@@ -56,6 +60,8 @@ export default function SettingsPage() {
       setUpcomingDays(settings.upcoming_days);
       setPreferredName(settings.preferred_name ?? '');
       setFirstDayOfWeek(settings.first_day_of_week);
+      setAutoLockEnabled(settings.auto_lock_enabled);
+      setAutoLockMinutes(settings.auto_lock_minutes);
     }
   }, [settings?.id]); // only re-sync on initial load (settings.id won't change)
 
@@ -176,6 +182,31 @@ export default function SettingsPage() {
     }
   };
 
+  const handleAutoLockToggle = async (checked: boolean) => {
+    const previous = autoLockEnabled;
+    setAutoLockEnabled(checked);
+    try {
+      await updateSettings({ auto_lock_enabled: checked });
+      toast.success(checked ? 'Auto-lock enabled' : 'Auto-lock disabled');
+    } catch {
+      setAutoLockEnabled(previous);
+      toast.error('Failed to update auto-lock setting');
+    }
+  };
+
+  const handleAutoLockMinutesSave = async () => {
+    const clamped = Math.max(1, Math.min(60, autoLockMinutes || 5));
+    setAutoLockMinutes(clamped);
+    if (clamped === settings?.auto_lock_minutes) return;
+    try {
+      await updateSettings({ auto_lock_minutes: clamped });
+      toast.success(`Auto-lock timeout set to ${clamped} minutes`);
+    } catch {
+      setAutoLockMinutes(settings?.auto_lock_minutes ?? 5);
+      toast.error('Failed to update auto-lock timeout');
+    }
+  };
+
   return (
     <div className="flex flex-col h-full">
       {/* Page header — matches Stage 4-5 pages */}
@@ -349,9 +380,56 @@ export default function SettingsPage() {
 
             </div>
 
-            {/* ── Right column: Authentication, Calendar, Dashboard, Integrations ── */}
+            {/* ── Right column: Security, Authentication, Calendar, Dashboard, Integrations ── */}
             <div className="space-y-6">
 
+              {/* Security (auto-lock) */}
+              <Card>
+                <CardHeader>
+                  <div className="flex items-center gap-3">
+                    <div className="p-1.5 rounded-md bg-emerald-500/10">
+                      <Shield className="h-4 w-4 text-emerald-400" aria-hidden="true" />
+                    </div>
+                    <div>
+                      <CardTitle>Security</CardTitle>
+                      <CardDescription>Configure screen lock behavior</CardDescription>
+                    </div>
+                  </div>
+                </CardHeader>
+                <CardContent className="space-y-4">
+                  <div className="flex items-center justify-between">
+                    <div className="space-y-0.5">
+                      <Label>Auto-lock</Label>
+                      <p className="text-sm text-muted-foreground">
+                        Automatically lock the screen after idle time
+                      </p>
+                    </div>
+                    <Switch
+                      checked={autoLockEnabled}
+                      onCheckedChange={handleAutoLockToggle}
+                    />
+                  </div>
+                  <div className="space-y-2">
+                    <Label htmlFor="auto_lock_minutes">Lock after</Label>
+                    <div className="flex gap-3 items-center">
+                      <Input
+                        id="auto_lock_minutes"
+                        type="number"
+                        min="1"
+                        max="60"
+                        value={autoLockMinutes}
+                        onChange={(e) => setAutoLockMinutes(parseInt(e.target.value) || 5)}
+                        onBlur={handleAutoLockMinutesSave}
+                        onKeyDown={(e) => { if (e.key === 'Enter') handleAutoLockMinutesSave(); }}
+                        className="w-24"
+                        disabled={!autoLockEnabled || isUpdating}
+                      />
+                      <span className="text-sm text-muted-foreground">minutes</span>
+                    </div>
+                  </div>
+                </CardContent>
+              </Card>
+
               {/* Authentication (TOTP + password change) */}
               <TotpSetupSection />
 
diff --git a/frontend/src/hooks/useLock.tsx b/frontend/src/hooks/useLock.tsx
new file mode 100644
index 0000000..4dc01f4
--- /dev/null
+++ b/frontend/src/hooks/useLock.tsx
@@ -0,0 +1,108 @@
+import {
+  createContext,
+  useContext,
+  useState,
+  useCallback,
+  useEffect,
+  useRef,
+  type ReactNode,
+} from 'react';
+import { useIsMutating } from '@tanstack/react-query';
+import { useSettings } from '@/hooks/useSettings';
+import api from '@/lib/api';
+
+interface LockContextValue {
+  isLocked: boolean;
+  lock: () => void;
+  unlock: (password: string) => Promise<void>;
+}
+
+const LockContext = createContext<LockContextValue | null>(null);
+
+const ACTIVITY_EVENTS = ['mousemove', 'keydown', 'click', 'scroll', 'touchstart'] as const;
+const THROTTLE_MS = 5_000; // only reset timer every 5s of activity
+
+export function LockProvider({ children }: { children: ReactNode }) {
+  const [isLocked, setIsLocked] = useState(false);
+  const { settings } = useSettings();
+  const activeMutations = useIsMutating();
+
+  const timerRef = useRef<ReturnType<typeof setTimeout> | null>(null);
+  const lastActivityRef = useRef<number>(Date.now());
+
+  const lock = useCallback(() => {
+    setIsLocked(true);
+  }, []);
+
+  const unlock = useCallback(async (password: string) => {
+    const { data } = await api.post<{ verified: boolean }>('/auth/verify-password', { password });
+    if (data.verified) {
+      setIsLocked(false);
+      lastActivityRef.current = Date.now();
+    }
+  }, []);
+
+  // Auto-lock idle timer
+  useEffect(() => {
+    const enabled = settings?.auto_lock_enabled ?? false;
+    const minutes = settings?.auto_lock_minutes ?? 5;
+
+    if (!enabled || isLocked) {
+      // Clear any existing timer when disabled or already locked
+      if (timerRef.current) {
+        clearTimeout(timerRef.current);
+        timerRef.current = null;
+      }
+      return;
+    }
+
+    const timeoutMs = minutes * 60_000;
+
+    const resetTimer = () => {
+      // Don't lock while TanStack mutations are in flight
+      if (activeMutations > 0) return;
+
+      if (timerRef.current) clearTimeout(timerRef.current);
+      timerRef.current = setTimeout(() => {
+        lock();
+      }, timeoutMs);
+    };
+
+    const handleActivity = () => {
+      const now = Date.now();
+      if (now - lastActivityRef.current < THROTTLE_MS) return;
+      lastActivityRef.current = now;
+      resetTimer();
+    };
+
+    // Start the initial timer
+    resetTimer();
+
+    // Attach throttled listeners
+    for (const event of ACTIVITY_EVENTS) {
+      document.addEventListener(event, handleActivity, { passive: true });
+    }
+
+    return () => {
+      for (const event of ACTIVITY_EVENTS) {
+        document.removeEventListener(event, handleActivity);
+      }
+      if (timerRef.current) {
+        clearTimeout(timerRef.current);
+        timerRef.current = null;
+      }
+    };
+  }, [settings?.auto_lock_enabled, settings?.auto_lock_minutes, isLocked, lock, activeMutations]);
+
+  return (
+    <LockContext.Provider value={{ isLocked, lock, unlock }}>
+      {children}
+    </LockContext.Provider>
+  );
+}
+
+export function useLock(): LockContextValue {
+  const ctx = useContext(LockContext);
+  if (!ctx) throw new Error('useLock must be used within a LockProvider');
+  return ctx;
+}
diff --git a/frontend/src/index.css b/frontend/src/index.css
index 0d599e2..508f5b1 100644
--- a/frontend/src/index.css
+++ b/frontend/src/index.css
@@ -192,3 +192,47 @@
   color: hsl(var(--accent-color));
   font-weight: 600;
 }
+
+/* ── Ambient background animations ── */
+
+@keyframes drift-1 {
+  0%, 100% { transform: translate(0, 0); }
+  25% { transform: translate(60px, 40px); }
+  50% { transform: translate(-30px, 80px); }
+  75% { transform: translate(40px, -20px); }
+}
+
+@keyframes drift-2 {
+  0%, 100% { transform: translate(0, 0); }
+  25% { transform: translate(-50px, -30px); }
+  50% { transform: translate(40px, -60px); }
+  75% { transform: translate(-20px, 40px); }
+}
+
+@keyframes drift-3 {
+  0%, 100% { transform: translate(0, 0); }
+  33% { transform: translate(30px, -50px); }
+  66% { transform: translate(-40px, 30px); }
+}
+
+@keyframes slide-up {
+  from {
+    opacity: 0;
+    transform: translateY(16px);
+  }
+  to {
+    opacity: 1;
+    transform: translateY(0);
+  }
+}
+
+@keyframes fade-in {
+  from { opacity: 0; }
+  to { opacity: 1; }
+}
+
+.animate-drift-1 { animation: drift-1 25s ease-in-out infinite; }
+.animate-drift-2 { animation: drift-2 30s ease-in-out infinite; }
+.animate-drift-3 { animation: drift-3 20s ease-in-out infinite; }
+.animate-slide-up { animation: slide-up 0.5s ease-out both; }
+.animate-fade-in { animation: fade-in 0.3s ease-out both; }
diff --git a/frontend/src/types/index.ts b/frontend/src/types/index.ts
index 7ec14b2..b47ec34 100644
--- a/frontend/src/types/index.ts
+++ b/frontend/src/types/index.ts
@@ -19,6 +19,9 @@ export interface Settings {
   ntfy_todo_lead_days: number;
   ntfy_project_lead_days: number;
   ntfy_has_token: boolean;
+  // Auto-lock settings
+  auto_lock_enabled: boolean;
+  auto_lock_minutes: number;
   created_at: string;
   updated_at: string;
 }