diff --git a/backend/workflows/static/workflows/js/session_warning.js b/backend/workflows/static/workflows/js/session_warning.js
index ae7eff5..6ea9ca5 100644
--- a/backend/workflows/static/workflows/js/session_warning.js
+++ b/backend/workflows/static/workflows/js/session_warning.js
@@ -11,6 +11,10 @@
   const extendButton = document.getElementById("app-session-warning-extend");
   if (!modal || !countdown || !extendButton || !status || !orb || !orbValue) return;
 
+  const storageKey = "workdock.session.lastConfirmedAt";
+  const syncChannel = typeof BroadcastChannel !== "undefined"
+    ? new BroadcastChannel("workdock-session-warning")
+    : null;
   let lastConfirmedAt = Date.now();
   let warningVisible = false;
   let keepaliveInFlight = false;
@@ -40,6 +44,32 @@
     status.textContent = "";
   }
 
+  function readStoredConfirmedAt() {
+    try {
+      const raw = window.localStorage.getItem(storageKey);
+      const parsed = raw ? Number.parseInt(raw, 10) : NaN;
+      return Number.isFinite(parsed) ? parsed : null;
+    } catch (_error) {
+      return null;
+    }
+  }
+
+  function syncConfirmedAt(timestamp, source) {
+    lastConfirmedAt = timestamp;
+    try {
+      window.localStorage.setItem(storageKey, String(timestamp));
+    } catch (_error) {
+      // Ignore storage write failures.
+    }
+    if (syncChannel && source !== "broadcast") {
+      syncChannel.postMessage({ type: "confirmed-at", value: timestamp });
+    }
+    if (source !== "self") {
+      hideWarning();
+      hideStatus();
+    }
+  }
+
   function showWarning(secondsLeft) {
     countdown.textContent = `Noch etwa ${secondsLeft} Sekunden bis zur automatischen Abmeldung.`;
     orb.style.setProperty("--session-warning-progress", String(Math.max(0, Math.min(1, secondsLeft / warningLeadSeconds))));
@@ -69,7 +99,7 @@
         window.location.href = config.loginUrl;
         return;
       }
-      lastConfirmedAt = Date.now();
+      syncConfirmedAt(Date.now(), "self");
       showStatus("Sitzung erfolgreich verlängert.");
       orb.style.setProperty("--session-warning-progress", "1");
       orbValue.textContent = "OK";
@@ -84,6 +114,37 @@
     }
   }
 
+  const storedConfirmedAt = readStoredConfirmedAt();
+  if (storedConfirmedAt) {
+    lastConfirmedAt = storedConfirmedAt;
+  } else {
+    syncConfirmedAt(lastConfirmedAt, "self");
+  }
+
+  if (syncChannel) {
+    syncChannel.addEventListener("message", function (event) {
+      if (event.data && event.data.type === "confirmed-at" && Number.isFinite(event.data.value)) {
+        syncConfirmedAt(event.data.value, "broadcast");
+      }
+    });
+  }
+
+  window.addEventListener("storage", function (event) {
+    if (event.key !== storageKey || !event.newValue) return;
+    const parsed = Number.parseInt(event.newValue, 10);
+    if (Number.isFinite(parsed)) {
+      syncConfirmedAt(parsed, "storage");
+    }
+  });
+
+  document.addEventListener("visibilitychange", function () {
+    if (document.visibilityState !== "visible") return;
+    const latest = readStoredConfirmedAt();
+    if (latest && latest > lastConfirmedAt) {
+      syncConfirmedAt(latest, "storage");
+    }
+  });
+
   function tick() {
     const elapsedSeconds = Math.floor((Date.now() - lastConfirmedAt) / 1000);
     const secondsLeft = config.idleTimeoutSeconds - elapsedSeconds;
diff --git a/backend/workflows/templates/workflows/developer_handbook.html b/backend/workflows/templates/workflows/developer_handbook.html
index 04b1318..afc41b1 100644
--- a/backend/workflows/templates/workflows/developer_handbook.html
+++ b/backend/workflows/templates/workflows/developer_handbook.html
@@ -846,6 +846,7 @@ make backup-verify BACKUP_DIR=backups/backup_YYYYmmdd_HHMMSS</code></pre>
         <li><code>SESSION_IDLE_TIMEOUT_SECONDS</code> controls the idle session window.</li>
         <li><code>SENSITIVE_ACTION_REAUTH_SECONDS</code> controls when sensitive POST actions require fresh authentication.</li>
         <li><code>/session/keepalive/</code> refreshes both session timestamps when the user chooses <code>Angemeldet bleiben</code>.</li>
+        <li>Open tabs now sync the confirmed session timestamp through browser storage and <code>BroadcastChannel</code>, so extending the session in one tab updates the warning state in the others.</li>
       </ul>
       <p>This warning is meant to protect work in progress without silently relaxing the security middleware.</p>
     </div>