diff --git a/app.js b/app.js
index 13321b7..5770bac 100644
--- a/app.js
+++ b/app.js
@@ -1230,7 +1230,11 @@ class DienstplanApp {
 
 // Initialize app when DOM is ready
 let app;
-document.addEventListener('DOMContentLoaded', () => {
+document.addEventListener('DOMContentLoaded', async () => {
+    if (window.DataSync) {
+        try { await window.DataSync.boot(); }
+        catch (e) { console.error('Sync-Boot fehlgeschlagen, App laeuft lokal weiter:', e); }
+    }
     app = new DienstplanApp();
     window.app = app;
 });
diff --git a/index.html b/index.html
index 1d76018..369f8bc 100644
--- a/index.html
+++ b/index.html
@@ -326,6 +326,7 @@
     <script src="variants.js"></script>
     <script src="calculator.js"></script>
     <script src="storage.js"></script>
+    <script src="sync.js"></script>
     <script src="app.js"></script>
     <script src="image-import.js"></script>
 </body>
diff --git a/storage.js b/storage.js
index ca67c99..c1d064d 100644
--- a/storage.js
+++ b/storage.js
@@ -45,6 +45,7 @@ class DataStorage {
                 throw new TypeError('employees muss ein Array sein');
             }
             localStorage.setItem(this.STORAGE_KEY_EMPLOYEES, JSON.stringify(employees));
+            this._notifyChange();
         } catch (e) {
             console.error('Fehler beim Speichern der Mitarbeiter-Daten:', e);
             throw e;
@@ -117,6 +118,7 @@ class DataStorage {
                 throw new TypeError('duties muss ein gültiges Objekt sein');
             }
             localStorage.setItem(this.STORAGE_KEY_DUTIES, JSON.stringify(duties));
+            this._notifyChange();
         } catch (e) {
             console.error('Fehler beim Speichern der Dienst-Daten:', e);
             throw e;
@@ -285,6 +287,7 @@ class DataStorage {
             if (!map[employeeName]) map[employeeName] = {};
             map[employeeName][yearMonth] = Boolean(value);
             localStorage.setItem(this.STORAGE_KEY_VACATION, JSON.stringify(map));
+            this._notifyChange();
         } catch (e) {
             console.error('Fehler beim Speichern des Urlaubsmodus:', e);
             throw e;
@@ -319,6 +322,16 @@ class DataStorage {
         return map;
     }
 
+    /**
+     * Signalisiert dem Sync-Layer eine Aenderung (falls vorhanden).
+     * Wird unterdrueckt, waehrend DataSync gerade Server-Daten uebernimmt.
+     */
+    _notifyChange() {
+        if (typeof window !== 'undefined' && window.DataSync && !window.DataSync._applying) {
+            window.DataSync.push();
+        }
+    }
+
     /**
      * Clear all data
      */
@@ -326,6 +339,7 @@ class DataStorage {
         localStorage.removeItem(this.STORAGE_KEY_EMPLOYEES);
         localStorage.removeItem(this.STORAGE_KEY_DUTIES);
         localStorage.removeItem(this.STORAGE_KEY_VACATION);
+        this._notifyChange();
     }
 
     /**
@@ -363,6 +377,7 @@ class DataStorage {
             if (data.vacation && typeof data.vacation === 'object') {
                 localStorage.setItem(this.STORAGE_KEY_VACATION, JSON.stringify(data.vacation));
             }
+            this._notifyChange();
             return true;
         } catch (e) {
             console.error('Import failed:', e);
diff --git a/sw.js b/sw.js
index d095496..ac3420d 100644
--- a/sw.js
+++ b/sw.js
@@ -1,4 +1,4 @@
-const CACHE_NAME = 'dienstplan-pro-v4';
+const CACHE_NAME = 'dienstplan-pro-v5';
 const ASSETS = [
   './',
   './index.html',
@@ -8,6 +8,7 @@ const ASSETS = [
   './variants.js',
   './holidays.js',
   './storage.js',
+  './sync.js',
   './image-import.js'
 ];