diff --git a/.phase18-state.json b/.phase18-state.json
index 0b6ba16..0ab1aed 100644
--- a/.phase18-state.json
+++ b/.phase18-state.json
@@ -1,8 +1,9 @@
 {
   "completed_features": [],
-  "current_feature": "audit-log-filters",
+  "current_feature": "idle-detection",
   "started_at": "2026-05-23T07:29:44.977564",
   "attempted_features": [
-    "api-key-management"
+    "api-key-management",
+    "audit-log-filters"
   ]
 }
\ No newline at end of file
diff --git a/GENERATION_LOG.md b/GENERATION_LOG.md
index c598c99..3091178 100644
--- a/GENERATION_LOG.md
+++ b/GENERATION_LOG.md
@@ -2171,3 +2171,22 @@ src/index.ts(27,25): error TS2769: No overload matches this call.
   Overload 2 of 3, '(plugin: FastifyPluginAsync<{ limits: { fileSize: number; }; }, RawServerDefault, FastifyTypeProvider, FastifyBaseLogger>, opts?: FastifyRegisterOptions<...> | undefined): FastifyInstance<...> & PromiseLike<...>', gave the following error.
     Argument of type 'Promise<FastifyMultipartPlugin>' is not assignable to parameter of type 'FastifyPluginAsync<{ limits: { fileSize: number; }; }, RawServerDefault, FastifyTypeProvider, FastifyBaseLogger>'.
       Type 'Promise<FastifyMultipartPlugin>' provides no match for the signature '(instance: FastifyInstance<RawServerDefault, IncomingMessage, ServerResponse<IncomingMessage>, FastifyBaseLogger, FastifyTy
+- `07:32:56` **INFO**   Committed feature audit-log-filters
+- `07:32:57` **INFO**   Pushed: rc=0
+
+## Phase-3 Feature: idle-detection (2026-05-23 07:32:57)
+
+- `07:32:57` **INFO** Description: Idle-Detection: nach 5min Inaktivität Active-Timer pausieren-prompt
+- `07:32:57` **INFO**   Generating apps/web/src/components/IdleDetector.tsx (IdleDetector-Component. Listens auf mousemove, keypress. Resettet Time…)
+- `07:33:28` **INFO**     wrote 3511 chars in 31.4s (attempt 1)
+- `07:33:28` **INFO**   Generating apps/web/src/App.tsx (ERWEITERT — mount <IdleDetector /> global im Root-Route. Behalte alles…)
+- `07:34:22` **INFO**     wrote 6578 chars in 54.2s (attempt 1)
+- `07:34:22` **INFO** Running tsc --noEmit on api…
+- `07:34:24` **WARN**   tsc errors:
+src/index.ts(27,25): error TS2769: No overload matches this call.
+  Overload 1 of 3, '(plugin: FastifyPluginCallback<{ limits: { fileSize: number; }; }, RawServerDefault, FastifyTypeProvider, FastifyBaseLogger>, opts?: FastifyRegisterOptions<...> | undefined): FastifyInstance<...> & PromiseLike<...>', gave the following error.
+    Argument of type 'Promise<FastifyMultipartPlugin>' is not assignable to parameter of type 'FastifyPluginCallback<{ limits: { fileSize: number; }; }, RawServerDefault, FastifyTypeProvider, FastifyBaseLogger>'.
+      Type 'Promise<FastifyMultipartPlugin>' provides no match for the signature '(instance: FastifyInstance<RawServerDefault, IncomingMessage, ServerResponse<IncomingMessage>, FastifyBaseLogger, FastifyTypeProvider>, opts: { ...; }, done: (err?: Error | undefined) => void): void'.
+  Overload 2 of 3, '(plugin: FastifyPluginAsync<{ limits: { fileSize: number; }; }, RawServerDefault, FastifyTypeProvider, FastifyBaseLogger>, opts?: FastifyRegisterOptions<...> | undefined): FastifyInstance<...> & PromiseLike<...>', gave the following error.
+    Argument of type 'Promise<FastifyMultipartPlugin>' is not assignable to parameter of type 'FastifyPluginAsync<{ limits: { fileSize: number; }; }, RawServerDefault, FastifyTypeProvider, FastifyBaseLogger>'.
+      Type 'Promise<FastifyMultipartPlugin>' provides no match for the signature '(instance: FastifyInstance<RawServerDefault, IncomingMessage, ServerResponse<IncomingMessage>, FastifyBaseLogger, FastifyTy
diff --git a/apps/web/src/App.tsx b/apps/web/src/App.tsx
index cca8b40..f299122 100644
--- a/apps/web/src/App.tsx
+++ b/apps/web/src/App.tsx
@@ -26,6 +26,7 @@ import KeyboardHelp from "./components/KeyboardHelp"
 import OnboardingTour from "./components/OnboardingTour"
 import VersionBadge from "./components/VersionBadge"
 import QuickAdd from "./components/QuickAdd"
+import IdleDetector from "./components/IdleDetector"
 import { ToastProvider } from "./components/Toast"
 import ErrorBoundary from "./components/ErrorBoundary"
 import { api } from "./lib/api"
@@ -35,6 +36,7 @@ const rootRoute = createRootRoute({
     <ToastProvider>
       <div className="min-h-screen flex flex-col bg-slate-50">
         <div className="flex-grow">
+          <IdleDetector />
           <Nav />
           <CommandPalette />
           <KeyboardHelp />
@@ -150,13 +152,6 @@ const documentsRoute = createRoute({
   component: Documents
 })
 
-const invoicesRoute = createRoute({
-  getParentRoute: () => rootRoute,
-  path: "/invoices",
-  beforeLoad: authCheck,
-  component: Invoices
-})
-
 const profileRoute = createRoute({
   getParentRoute: () => rootRoute,
   path: "/profile",
@@ -164,13 +159,6 @@ const profileRoute = createRoute({
   component: Profile
 })
 
-const twoFactorRoute = createRoute({
-  getParentRoute: () => rootRoute,
-  path: "/two-factor",
-  beforeLoad: authCheck,
-  component: TwoFactorAuth
-})
-
 const settingsRoute = createRoute({
   getParentRoute: () => rootRoute,
   path: "/settings",
@@ -178,6 +166,43 @@ const settingsRoute = createRoute({
   component: Settings
 })
 
+const adminUsersRoute = createRoute({
+  getParentRoute: () => rootRoute,
+  path: "/admin/users",
+  beforeLoad: async () => {
+    await authCheck()
+    await adminCheck()
+  },
+  component: AdminUsers
+})
+
+const auditLogRoute = createRoute({
+  getParentRoute: () => rootRoute,
+  path: "/admin/audit-log",
+  beforeLoad: async () => {
+    await authCheck()
+    await adminCheck()
+  },
+  component: AuditLog
+})
+
+const webhooksRoute = createRoute({
+  getParentRoute: () => rootRoute,
+  path: "/admin/webhooks",
+  beforeLoad: async () => {
+    await authCheck()
+    await adminCheck()
+  },
+  component: Webhooks
+})
+
+const twoFactorRoute = createRoute({
+  getParentRoute: () => rootRoute,
+  path: "/settings/2fa",
+  beforeLoad: authCheck,
+  component: TwoFactorAuth
+})
+
 const billingRoute = createRoute({
   getParentRoute: () => rootRoute,
   path: "/billing",
@@ -194,30 +219,19 @@ const integrationsRoute = createRoute({
 
 const projectTemplatesRoute = createRoute({
   getParentRoute: () => rootRoute,
-  path: "/project-templates",
-  beforeLoad: authCheck,
+  path: "/admin/project-templates",
+  beforeLoad: async () => {
+    await authCheck()
+    await adminCheck()
+  },
   component: ProjectTemplates
 })
 
-const adminUsersRoute = createRoute({
+const invoicesRoute = createRoute({
   getParentRoute: () => rootRoute,
-  path: "/admin/users",
-  beforeLoad: adminCheck,
-  component: AdminUsers
-})
-
-const auditLogRoute = createRoute({
-  getParentRoute: () => rootRoute,
-  path: "/admin/audit-log",
-  beforeLoad: adminCheck,
-  component: AuditLog
-})
-
-const webhooksRoute = createRoute({
-  getParentRoute: () => rootRoute,
-  path: "/admin/webhooks",
-  beforeLoad: adminCheck,
-  component: Webhooks
+  path: "/invoices",
+  beforeLoad: authCheck,
+  component: Invoices
 })
 
 const routeTree = [
@@ -232,21 +246,21 @@ const routeTree = [
   projectsRoute,
   projectDetailRoute,
   documentsRoute,
-  invoicesRoute,
   profileRoute,
-  twoFactorRoute,
   settingsRoute,
-  billingRoute,
-  integrationsRoute,
-  projectTemplatesRoute,
   adminUsersRoute,
   auditLogRoute,
   webhooksRoute,
+  twoFactorRoute,
+  billingRoute,
+  integrationsRoute,
+  projectTemplatesRoute,
+  invoicesRoute
 ]
 
 const router = createRouter({ 
   routeTree,
-  defaultCatcher: (error) => <ErrorBoundary error={error} />
+  defaultPreload: 'intent'
 })
 
 declare module "@tanstack/react-router" {
@@ -256,5 +270,9 @@ declare module "@tanstack/react-router" {
 }
 
 export default function App() {
-  return <RouterProvider router={router} />
+  return (
+    <ErrorBoundary>
+      <RouterProvider router={router} />
+    </ErrorBoundary>
+  )
 }
\ No newline at end of file
diff --git a/apps/web/src/components/IdleDetector.tsx b/apps/web/src/components/IdleDetector.tsx
new file mode 100644
index 0000000..d3b9997
--- /dev/null
+++ b/apps/web/src/components/IdleDetector.tsx
@@ -0,0 +1,95 @@
+import React, { useState, useEffect } from 'react'
+import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query'
+import { api } from '../lib/api'
+import { AlertCircle, Play, Square } from 'lucide-react'
+
+const IDLE_TIMEOUT = 5 * 60 * 1000 // 5 minutes
+
+export const IdleDetector = () => {
+  const queryClient = useQueryClient()
+  const [isIdle, setIsIdle] = useState(false)
+  const [timer, setTimer] = useState<NodeJS.Timeout | null>(null)
+
+  const { data: runningEntry } = useQuery({
+    queryKey: ['running-entry'],
+    queryFn: () => api.getRunningTimeEntry(),
+    refetchInterval: 30000,
+  })
+
+  const stopMutation = useMutation({
+    mutationFn: (id: string) => api.stopTimeEntry(id),
+    onSuccess: () => {
+      queryClient.invalidateQueries({ queryKey: ['running-entry'] })
+      setIsIdle(false)
+    },
+  })
+
+  const resetIdleTimer = () => {
+    if (timer) clearTimeout(timer)
+    setIsIdle(false)
+    
+    const newTimer = setTimeout(() => {
+      setIsIdle(true)
+    }, IDLE_TIMEOUT)
+    
+    setTimer(newTimer)
+  }
+
+  useEffect(() => {
+    const events = ['mousemove', 'mousedown', 'keydown', 'scroll', 'touchstart']
+    
+    const handleActivity = () => resetIdleTimer()
+
+    events.forEach(event => window.addEventListener(event, handleActivity))
+    resetIdleTimer()
+
+    return () => {
+      events.forEach(event => window.removeEventListener(event, handleActivity))
+      if (timer) clearTimeout(timer)
+    }
+  }, [])
+
+  // Only show modal if user is idle AND a timer is actually running
+  if (!isIdle || !runningEntry) return null
+
+  return (
+    <div className="fixed inset-0 z-50 flex items-center justify-center bg-slate-900/50 backdrop-blur-sm p-4">
+      <div className="bg-white dark:bg-slate-800 border border-slate-200 dark:border-slate-700 rounded-xl shadow-xl max-w-md w-full p-6 animate-in fade-in zoom-in duration-200">
+        <div className="flex items-start gap-4">
+          <div className="p-2 bg-amber-100 dark:bg-amber-900/30 rounded-full">
+            <AlertCircle className="w-6 h-6 text-amber-600 dark:text-amber-400" />
+          </div>
+          <div className="flex-1">
+            <h3 className="text-lg font-semibold text-slate-900 dark:text-white">
+              Are you still there?
+            </h3>
+            <p className="text-sm text-slate-500 dark:text-slate-400 mt-1">
+              You've been inactive for 5 minutes. Should we stop the timer for <span className="font-medium text-slate-700 dark:text-slate-200">"{runningEntry.description || 'this entry'}"</span>?
+            </p>
+          </div>
+        </div>
+
+        <div className="mt-6 flex gap-3 justify-end">
+          <button
+            onClick={() => {
+              resetIdleTimer()
+              setIsIdle(false)
+            }}
+            className="px-4 py-2 text-sm font-medium text-slate-700 dark:text-slate-200 hover:bg-slate-100 dark:hover:bg-slate-700 rounded-md transition-colors flex items-center gap-2"
+          >
+            <Play className="w-3 h-3 fill-current" />
+            Keep running
+          </button>
+          <button
+            onClick={() => stopMutation.mutate(runningEntry.id)}
+            disabled={stopMutation.isPending}
+            className="px-4 py-2 text-sm font-medium bg-red-600 hover:bg-red-700 text-white rounded-md transition-colors flex items-center gap-2 disabled:opacity-50"
+          >
+            <Square className="w-3 h-3 fill-current" />
+            Stop timer
+          </button>
+        </div>
+      </div>
+    </div>
+  )
+}
\ No newline at end of file