diff --git a/shop/components/inactivity-tracker.tsx b/shop/components/inactivity-tracker.tsx
index a7f0bb0..c9b902b 100644
--- a/shop/components/inactivity-tracker.tsx
+++ b/shop/components/inactivity-tracker.tsx
@@ -1,19 +1,40 @@
 "use client";
 
-import { useEffect } from "react";
+import { useEffect, useState, useRef, useCallback } from "react";
 import { createBrowserClient } from "@supabase/ssr";
 import { useRouter } from "next/navigation";
 import { signOut } from "@/lib/actions/auth";
 import { resolveSupabaseUrl } from "@/lib/utils";
+import {
+  Dialog,
+  DialogContent,
+  DialogHeader,
+  DialogTitle,
+  DialogDescription,
+  DialogFooter,
+} from "@/components/ui/dialog";
+import { Button } from "@/components/ui/button";
+import { Clock } from "lucide-react";
+
+// Inaktivitäts-Schwellenwert (10 Minuten = 600.000 ms)
+const INACTIVITY_TIMEOUT_MS = 10 * 60 * 1000;
+// Countdown-Dauer vor automatischem Logout (10 Sekunden)
+const COUNTDOWN_SECONDS = 10;
 
 export function InactivityTracker() {
   const router = useRouter();
 
+  const [isLoggedIn, setIsLoggedIn] = useState(false);
+  const [showModal, setShowModal] = useState(false);
+  const [countdown, setCountdown] = useState(COUNTDOWN_SECONDS);
+
+  const lastActivityRef = useRef<number>(Date.now());
+  const countdownIntervalRef = useRef<NodeJS.Timeout | null>(null);
+
   // Supabase URL & Anon Key auslesen (für Browser-Client)
   const supabaseUrl = process.env.SUPABASE_URL || process.env.NEXT_PUBLIC_SUPABASE_URL;
   const supabaseAnonKey = process.env.SUPABASE_ANON_KEY || process.env.NEXT_PUBLIC_SUPABASE_PUBLISHABLE_KEY || process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY;
 
-  // Browser Client inline erstellen
   const supabase = createBrowserClient(
     resolveSupabaseUrl(supabaseUrl)!,
     supabaseAnonKey!,
@@ -24,45 +45,216 @@ export function InactivityTracker() {
     }
   );
 
+  // Cookie-Hilfsfunktionen für Aktivitätssynchronisation mit dem Server
+  const updateLastActivityCookie = useCallback(() => {
+    const now = Date.now();
+    lastActivityRef.current = now;
+    document.cookie = `webshop-last-activity=${now}; path=/; SameSite=Lax`;
+  }, []);
+
+  const getLastActivityFromCookie = useCallback((): number => {
+    const match = document.cookie.match(/(?:^|; )webshop-last-activity=([^;]*)/);
+    if (match && match[1]) {
+      const val = parseInt(match[1], 10);
+      if (!isNaN(val)) return val;
+    }
+    return lastActivityRef.current;
+  }, []);
+
+  const handleLogout = useCallback(async (reason = "inactivity") => {
+    if (countdownIntervalRef.current) {
+      clearInterval(countdownIntervalRef.current);
+    }
+    setShowModal(false);
+    document.cookie = "webshop-last-activity=; path=/; max-age=0";
+    try {
+      await signOut();
+    } catch (e) {
+      console.error("Fehler beim Server-Signout:", e);
+    }
+    await supabase.auth.signOut();
+    router.push(`/auth/login?message=${reason}`);
+    router.refresh();
+  }, [supabase, router]);
+
+  // Session-Prüfung & Inaktivitäts-Überwachung
   useEffect(() => {
-    // Regelmäßige Überprüfung der Session-Gültigkeit (z.B. wegen Login auf anderem Browser/Gerät)
+    // 1. Session prüfen
+    const checkSession = async () => {
+      const { data: { session } } = await supabase.auth.getSession();
+      setIsLoggedIn(!!session);
+    };
+    checkSession();
+
+    // 2. Regelmäßige Intervall-Prüfung (alle 5s)
     const interval = setInterval(async () => {
       const { data: { session } } = await supabase.auth.getSession();
-      if (!session) return; // Nicht eingeloggt, keine Prüfung nötig
+      if (!session) {
+        setIsLoggedIn(false);
+        return;
+      }
+      setIsLoggedIn(true);
 
-      // Prüfen, ob die Session auf dem Server noch gültig ist (z.B. wegen Login auf anderem Browser)
+      // Prüfen, ob Session auf Server noch gültig ist
       const { data: { user }, error } = await supabase.auth.getUser();
       if (error) {
-        // Nur bei echten Auth-Fehlern (z.B. ungültiges Token / Session gelöscht) abmelden.
-        // Netzwerkfehler wie "Failed to fetch" haben keinen HTTP-Status (error.status ist undefined).
         const isAuthError = error.status === 400 || error.status === 401 || error.status === 403;
         if (isAuthError) {
-          try {
-            await signOut();
-          } catch (e) {
-            console.error("Fehler beim Server-Signout nach Session-Verlust:", e);
-          }
-          await supabase.auth.signOut();
-          router.push("/auth/login?message=concurrent");
-          router.refresh();
+          handleLogout("concurrent");
+          return;
         }
       } else if (!user) {
-        // Keine Fehlermeldung, aber auch kein User-Objekt (Sitzung abgelaufen/gelöscht)
-        try {
-          await signOut();
-        } catch (e) {
-          console.error("Fehler beim Server-Signout nach Session-Verlust:", e);
-        }
-        await supabase.auth.signOut();
-        router.push("/auth/login?message=concurrent");
-        router.refresh();
+        handleLogout("concurrent");
+        return;
       }
-    }, 5000); // Prüfung alle 5 Sekunden
+
+      // Inaktivitätszeitraum (Client + Cookie-Synchronisation) prüfen
+      const lastActive = getLastActivityFromCookie();
+      const now = Date.now();
+      if (!showModal && now - lastActive >= INACTIVITY_TIMEOUT_MS) {
+        setShowModal(true);
+        setCountdown(COUNTDOWN_SECONDS);
+      }
+    }, 5000);
 
     return () => {
       clearInterval(interval);
     };
-  }, [supabase, router]);
+  }, [supabase, handleLogout, showModal, getLastActivityFromCookie]);
 
-  return null;
+  // Aktivitätsevents registrieren
+  useEffect(() => {
+    if (!isLoggedIn) return;
+
+    let lastEventTime = 0;
+    const handleUserActivity = () => {
+      const now = Date.now();
+      // Throttling: max. 1x pro Sekunde aktualisieren
+      if (now - lastEventTime > 1000) {
+        lastEventTime = now;
+        // Wenn Modal bereits offen ist, Aktivität nicht im Hintergrund zurücksetzen
+        if (!showModal) {
+          updateLastActivityCookie();
+        }
+      }
+    };
+
+    const events = ["mousemove", "keydown", "click", "scroll", "touchstart"];
+    events.forEach((event) => {
+      window.addEventListener(event, handleUserActivity, { passive: true });
+    });
+
+    return () => {
+      events.forEach((event) => {
+        window.removeEventListener(event, handleUserActivity);
+      });
+    };
+  }, [isLoggedIn, showModal, updateLastActivityCookie]);
+
+  // Countdown-Timer verwalten, wenn Modal geöffnet wird
+  useEffect(() => {
+    if (!showModal) {
+      if (countdownIntervalRef.current) {
+        clearInterval(countdownIntervalRef.current);
+      }
+      return;
+    }
+
+    countdownIntervalRef.current = setInterval(() => {
+      setCountdown((prev) => {
+        if (prev <= 1) {
+          clearInterval(countdownIntervalRef.current!);
+          handleLogout("inactivity");
+          return 0;
+        }
+        return prev - 1;
+      });
+    }, 1000);
+
+    return () => {
+      if (countdownIntervalRef.current) {
+        clearInterval(countdownIntervalRef.current);
+      }
+    };
+  }, [showModal, handleLogout]);
+
+  // Inaktivität zurücksetzen / Modal schließen
+  const handleStayLoggedIn = () => {
+    updateLastActivityCookie();
+    setShowModal(false);
+    if (countdownIntervalRef.current) {
+      clearInterval(countdownIntervalRef.current);
+    }
+  };
+
+  if (!isLoggedIn) return null;
+
+  // Werte für den radialen SVG-Timer (Kreisumfang)
+  const radius = 40;
+  const circumference = 2 * Math.PI * radius;
+  const strokeDashoffset = circumference - (countdown / COUNTDOWN_SECONDS) * circumference;
+
+  return (
+    <Dialog open={showModal} onOpenChange={(open) => { if (!open) handleStayLoggedIn(); }}>
+      <DialogContent showCloseButton={false} className="sm:max-w-md text-center flex flex-col items-center gap-6 p-8">
+        <DialogHeader className="items-center text-center">
+          <div className="w-12 h-12 rounded-full bg-amber-500/10 text-amber-500 flex items-center justify-center mb-2">
+            <Clock className="w-6 h-6 animate-pulse" />
+          </div>
+          <DialogTitle className="text-xl font-bold text-foreground">
+            Noch da?
+          </DialogTitle>
+          <DialogDescription className="text-muted-foreground text-sm max-w-xs mt-1">
+            Sie sind seit längerem inaktiv. Aus Sicherheitsgründen werden Sie gleich abgemeldet.
+          </DialogDescription>
+        </DialogHeader>
+
+        {/* Radialer SVG-Timer */}
+        <div className="relative flex items-center justify-center my-2">
+          <svg className="w-32 h-32 transform -rotate-90" viewBox="0 0 100 100">
+            {/* Hintergrundkreis */}
+            <circle
+              cx="50"
+              cy="50"
+              r={radius}
+              className="stroke-muted/20"
+              strokeWidth="8"
+              fill="transparent"
+            />
+            {/* Countdown-Fortschrittskreis */}
+            <circle
+              cx="50"
+              cy="50"
+              r={radius}
+              className="stroke-amber-500 transition-all duration-1000 ease-linear"
+              strokeWidth="8"
+              strokeDasharray={circumference}
+              strokeDashoffset={strokeDashoffset}
+              strokeLinecap="round"
+              fill="transparent"
+            />
+          </svg>
+          {/* Numerische Restzeit in Sekunden */}
+          <div className="absolute inset-0 flex flex-col items-center justify-center">
+            <span className="text-3xl font-extrabold text-foreground tracking-tight">
+              {countdown}s
+            </span>
+            <span className="text-[10px] text-muted-foreground uppercase tracking-widest font-semibold mt-0.5">
+              Verbleibend
+            </span>
+          </div>
+        </div>
+
+        <DialogFooter className="w-full sm:justify-center">
+          <Button
+            onClick={handleStayLoggedIn}
+            className="w-full sm:w-auto px-8 bg-amber-500 hover:bg-amber-600 text-black font-semibold shadow-lg shadow-amber-500/20"
+          >
+            Ich bin noch da
+          </Button>
+        </DialogFooter>
+      </DialogContent>
+    </Dialog>
+  );
 }
+
diff --git a/shop/lib/supabase/proxy.ts b/shop/lib/supabase/proxy.ts
index 50f87d3..63d3037 100644
--- a/shop/lib/supabase/proxy.ts
+++ b/shop/lib/supabase/proxy.ts
@@ -119,8 +119,34 @@ export async function updateSession(request: NextRequest) {
   //    the cookies!
   // 4. Finally:
   //    return myNewResponse
-  // If this is not done, you may be causing the browser and server to go out
-  // of sync and terminate the user's session prematurely!
+  // Inaktivitäts-Prüfung serverseitig (10 Minuten = 600.000 ms)
+  const INACTIVITY_TIMEOUT_MS = 10 * 60 * 1000;
+
+  if (user?.sub && !request.nextUrl.pathname.startsWith("/auth")) {
+    const lastActivityCookie = request.cookies.get("webshop-last-activity");
+    const now = Date.now();
+
+    if (lastActivityCookie?.value) {
+      const lastActivityTime = parseInt(lastActivityCookie.value, 10);
+      if (!isNaN(lastActivityTime) && now - lastActivityTime > INACTIVITY_TIMEOUT_MS) {
+        // Länger als 10 Minuten inaktiv -> Auf dem Server sofort abmelden
+        const url = request.nextUrl.clone();
+        url.pathname = "/auth/login";
+        url.searchParams.set("message", "inactivity");
+        const response = NextResponse.redirect(url);
+        response.cookies.delete("webshop-auth-token");
+        response.cookies.delete("webshop-last-activity");
+        return response;
+      }
+    }
+
+    // Aktuellen Zeitstempel in Cookie schreiben
+    supabaseResponse.cookies.set("webshop-last-activity", now.toString(), {
+      path: "/",
+      sameSite: "lax",
+      httpOnly: false, // Für Client-Zugriff lesbar/schreibbar
+    });
+  }
 
   return supabaseResponse;
 }