diff --git a/backend/src/index.js b/backend/src/index.js
index 51c0d8d..9eaab84 100644
--- a/backend/src/index.js
+++ b/backend/src/index.js
@@ -6,11 +6,12 @@ import { gridRoutes } from './routes/grid.js'
 import { settingsRoutes } from './routes/settings.js'
 
 const app = Fastify({ logger: true, trustProxy: true })
+const startedAt = Date.now()
 
 await app.register(cookie)
 await app.register(cors, { origin: process.env.CORS_ORIGIN || false, credentials: true })
 
-app.get('/health', async () => ({ status: 'healthy' }))
+app.get('/health', async () => ({ status: 'healthy', version: process.env.BUILD_VERSION || String(startedAt) }))
 
 await app.register(gridRoutes)
 await app.register(settingsRoutes)
diff --git a/frontend/src/App.tsx b/frontend/src/App.tsx
index 9c8809d..833300f 100644
--- a/frontend/src/App.tsx
+++ b/frontend/src/App.tsx
@@ -1,5 +1,7 @@
 import { BrowserRouter, Routes, Route, Navigate } from 'react-router-dom'
 import { AuthGate } from './components/AuthGate'
+import { UpdateBanner } from './components/UpdateBanner'
+import { useVersionCheck } from './hooks/useVersionCheck'
 import { Layout } from './components/Layout'
 import { TwinOptimiser } from './pages/TwinOptimiser'
 import { Settings } from './pages/Settings'
@@ -18,11 +20,15 @@ function AppRoutes({ user }: { user: User }) {
 }
 
 export default function App() {
+  const updateAvailable = useVersionCheck('/twin-optimiser/health')
   return (
-    <BrowserRouter basename="/twin-optimiser">
-      <AuthGate>
-        {user => <AppRoutes user={user} />}
-      </AuthGate>
-    </BrowserRouter>
+    <>
+      <BrowserRouter basename="/twin-optimiser">
+        <AuthGate>
+          {user => <AppRoutes user={user} />}
+        </AuthGate>
+      </BrowserRouter>
+      <UpdateBanner visible={updateAvailable} />
+    </>
   )
 }
diff --git a/frontend/src/components/UpdateBanner.tsx b/frontend/src/components/UpdateBanner.tsx
new file mode 100644
index 0000000..b492c67
--- /dev/null
+++ b/frontend/src/components/UpdateBanner.tsx
@@ -0,0 +1,44 @@
+import { RefreshCw } from 'lucide-react'
+
+export function UpdateBanner({ visible }: { visible: boolean }) {
+  if (!visible) return null
+  return (
+    <div style={{
+      position: 'fixed',
+      bottom: 0,
+      left: 0,
+      right: 0,
+      zIndex: 9999,
+      background: 'var(--sidebar)',
+      color: 'var(--text-light)',
+      display: 'flex',
+      alignItems: 'center',
+      justifyContent: 'center',
+      gap: '12px',
+      padding: '10px 16px',
+      fontSize: '14px',
+      boxShadow: '0 -2px 8px rgba(0,0,0,0.3)',
+    }}>
+      <span>A new version is available.</span>
+      <button
+        onClick={() => window.location.reload()}
+        style={{
+          display: 'flex',
+          alignItems: 'center',
+          gap: '6px',
+          background: 'var(--accent)',
+          color: 'var(--sidebar)',
+          border: 'none',
+          borderRadius: '4px',
+          padding: '6px 14px',
+          fontWeight: 600,
+          cursor: 'pointer',
+          fontSize: '13px',
+        }}
+      >
+        <RefreshCw size={14} strokeWidth={1.75} />
+        Reload
+      </button>
+    </div>
+  )
+}
diff --git a/frontend/src/hooks/useVersionCheck.ts b/frontend/src/hooks/useVersionCheck.ts
new file mode 100644
index 0000000..e4fed28
--- /dev/null
+++ b/frontend/src/hooks/useVersionCheck.ts
@@ -0,0 +1,43 @@
+import { useEffect, useState } from 'react'
+
+const POLL_MS = 2 * 60 * 1000
+
+export function useVersionCheck(healthUrl: string) {
+  const [updateAvailable, setUpdateAvailable] = useState(false)
+
+  useEffect(() => {
+    let seenVersion: string | null = null
+
+    async function check() {
+      try {
+        const res = await fetch(healthUrl, { cache: 'no-store' })
+        if (!res.ok) return
+        const data = await res.json()
+        const v: string | undefined = data.version
+        if (!v) return
+        if (seenVersion === null) {
+          seenVersion = v
+        } else if (v !== seenVersion) {
+          setUpdateAvailable(true)
+        }
+      } catch {
+        // network error — skip silently
+      }
+    }
+
+    check()
+    const interval = setInterval(check, POLL_MS)
+
+    function onVisible() {
+      if (document.visibilityState === 'visible') check()
+    }
+    document.addEventListener('visibilitychange', onVisible)
+
+    return () => {
+      clearInterval(interval)
+      document.removeEventListener('visibilitychange', onVisible)
+    }
+  }, [healthUrl])
+
+  return updateAvailable
+}