diff --git a/frontend/src/components/AuthGate.tsx b/frontend/src/components/AuthGate.tsx
index e624df4..ebe16dd 100644
--- a/frontend/src/components/AuthGate.tsx
+++ b/frontend/src/components/AuthGate.tsx
@@ -1,6 +1,12 @@
-import { useEffect, useState } from 'react'
+import { useEffect, useRef, useState } from 'react'
 import type { User } from '../types'
 
+const SHARED_TIMEOUT_MS = 10 * 60 * 1000
+
+function isSharedDevice() {
+  return document.cookie.split(';').some(c => c.trim() === 'hnf_shared_device=1')
+}
+
 interface Props {
   children: (user: User) => React.ReactNode
 }
@@ -23,6 +29,7 @@ export function AuthGate({ children }: Props) {
   const [password, setPassword] = useState('')
   const [error, setError] = useState('')
   const [loading, setLoading] = useState(false)
+  const timerRef = useRef<ReturnType<typeof setTimeout> | null>(null)
 
   useEffect(() => {
     fetch('/api/auth/verify?app=cashup', { credentials: 'include' })
@@ -33,6 +40,30 @@ export function AuthGate({ children }: Props) {
       .catch(() => setState('login'))
   }, [])
 
+  useEffect(() => {
+    if (state !== 'authed' || !isSharedDevice()) return
+
+    async function forceLogout() {
+      await fetch('/api/auth/logout', { method: 'POST', credentials: 'include' }).catch(() => {})
+      setUser(null)
+      setState('login')
+    }
+
+    function reset() {
+      if (timerRef.current) clearTimeout(timerRef.current)
+      timerRef.current = setTimeout(forceLogout, SHARED_TIMEOUT_MS)
+    }
+
+    const events = ['mousemove', 'keydown', 'click', 'touchstart'] as const
+    events.forEach(e => window.addEventListener(e, reset, { passive: true }))
+    reset()
+
+    return () => {
+      if (timerRef.current) clearTimeout(timerRef.current)
+      events.forEach(e => window.removeEventListener(e, reset))
+    }
+  }, [state])
+
   async function login(e: React.FormEvent) {
     e.preventDefault()
     setLoading(true)
diff --git a/frontend/src/components/Layout.tsx b/frontend/src/components/Layout.tsx
index 08e0537..f830a89 100644
--- a/frontend/src/components/Layout.tsx
+++ b/frontend/src/components/Layout.tsx
@@ -45,7 +45,7 @@ export function Layout({ user, children }: Props) {
           <p style={{ color: 'var(--text-muted)', fontSize: '0.75rem', marginTop: '0.25rem' }}>{user.name}</p>
         </div>
 
-        <div style={{ flex: 1, padding: '0.5rem 0', overflowY: 'auto' }}>
+        <div className="nav-scroll" style={{ flex: 1, padding: '0.5rem 0', overflowY: 'auto' }}>
           {navItems.filter(item => !item.cap || can(user, item.cap)).map(({ to, label, icon: Icon }) => (
             <NavLink key={to} to={to} style={({ isActive }) => ({
               display: 'flex', alignItems: 'center', gap: '0.625rem',
diff --git a/frontend/src/index.css b/frontend/src/index.css
index 02145b4..29f6a49 100644
--- a/frontend/src/index.css
+++ b/frontend/src/index.css
@@ -35,6 +35,21 @@ body {
 button { cursor: pointer; font-family: inherit; }
 input, textarea, select { font-family: inherit; }
 
+/* Sidebar scrollbar */
+.nav-scroll::-webkit-scrollbar,
+.sidebar::-webkit-scrollbar,
+.sidebar-nav::-webkit-scrollbar { width: 4px; }
+.nav-scroll::-webkit-scrollbar-track,
+.sidebar::-webkit-scrollbar-track,
+.sidebar-nav::-webkit-scrollbar-track { background: transparent; }
+.nav-scroll::-webkit-scrollbar-thumb,
+.sidebar::-webkit-scrollbar-thumb,
+.sidebar-nav::-webkit-scrollbar-thumb { background: rgba(201,168,76,0.35); border-radius: 2px; }
+.nav-scroll::-webkit-scrollbar-thumb:hover,
+.sidebar::-webkit-scrollbar-thumb:hover,
+.sidebar-nav::-webkit-scrollbar-thumb:hover { background: rgba(201,168,76,0.65); }
+.nav-scroll, .sidebar, .sidebar-nav { scrollbar-width: thin; scrollbar-color: rgba(201,168,76,0.35) transparent; }
+
 @media print {
   nav { display: none !important; }
   main { overflow: visible !important; }
diff --git a/frontend/src/pages/Settings.tsx b/frontend/src/pages/Settings.tsx
index 61f27c1..ecd7fbf 100644
--- a/frontend/src/pages/Settings.tsx
+++ b/frontend/src/pages/Settings.tsx
@@ -5,6 +5,16 @@ import { can, fmtGBP, type User } from '../types'
 
 const DEFAULT_MACHINE_NAMES = ['Front Desk', 'Restaurant / Bar']
 
+function isSharedDevice() {
+  return document.cookie.split(';').some(c => c.trim() === 'hnf_shared_device=1')
+}
+
+function setSharedDeviceCookie(shared: boolean) {
+  document.cookie = shared
+    ? 'hnf_shared_device=1; max-age=31536000; path=/; SameSite=Strict'
+    : 'hnf_shared_device=; max-age=0; path=/; SameSite=Strict'
+}
+
 interface SettingsData {
   default_report_days: string
   petty_cash_float: string
@@ -42,6 +52,7 @@ export function SettingsPage({ user }: { user: User }) {
   const [testing, setTesting] = useState(false)
   const [refreshing, setRefreshing] = useState(false)
   const [msg, setMsg] = useState<{ text: string; ok: boolean } | null>(null)
+  const [isShared, setIsShared] = useState(isSharedDevice)
 
   function flash(text: string, ok = true) {
     setMsg({ text, ok })
@@ -332,6 +343,31 @@ export function SettingsPage({ user }: { user: User }) {
         </Card>
       )}
 
+      <Card style={{ marginBottom: '1rem' }}>
+        <div style={{ display: 'flex', justifyContent: 'space-between', alignItems: 'center' }}>
+          <div>
+            <h2 style={{ fontSize: '1rem', fontWeight: 700 }}>This Device</h2>
+            <p style={{ fontSize: '0.8rem', color: 'var(--text-mid)', marginTop: '0.25rem' }}>
+              {isShared
+                ? 'Marked as a shared computer — sessions time out after 10 minutes of inactivity.'
+                : 'Mark this as a shared computer to automatically log out after 10 minutes of inactivity.'}
+            </p>
+          </div>
+          <Btn
+            variant={isShared ? 'danger' : 'secondary'}
+            small
+            onClick={() => {
+              const next = !isShared
+              setSharedDeviceCookie(next)
+              setIsShared(next)
+              flash(next ? 'This device is now marked as shared.' : 'Shared device mode removed.')
+            }}
+          >
+            {isShared ? 'Remove Shared Status' : 'Mark as Shared'}
+          </Btn>
+        </div>
+      </Card>
+
       <Btn onClick={save} disabled={saving}>
         {saving ? 'Saving…' : 'Save Settings'}
       </Btn>