diff --git a/extension/audio-options.js b/extension/audio-options.js
index a45d4fa..5342377 100644
--- a/extension/audio-options.js
+++ b/extension/audio-options.js
@@ -126,17 +126,13 @@ function setCustomParam(param, value) {
 }
 
 async function init() {
-    let audioData = (await chrome.storage.local.get(['audioSettings'])).audioSettings;
-    const syncData = await chrome.storage.sync.get(['audioSettings', 'locale']);
-    if (!audioData && syncData.audioSettings) {
-        audioData = syncData.audioSettings;
-        await chrome.storage.local.set({ audioSettings: audioData });
-    }
-    const lang = syncData.locale || getSystemLanguage();
+    // Local-only: audioSettings/locale are never read from storage.sync.
+    const { audioSettings, locale } = await chrome.storage.local.get(['audioSettings', 'locale']);
+    const lang = locale || getSystemLanguage();
     await loadLocale(lang);
     translateDOM();
 
-    currentSettings = mergeAudioSettings(audioData);
+    currentSettings = mergeAudioSettings(audioSettings);
     render();
 }
 
diff --git a/extension/background.js b/extension/background.js
index 3d668d6..14a7887 100644
--- a/extension/background.js
+++ b/extension/background.js
@@ -43,11 +43,13 @@ async function initUninstallURL() {
 chrome.runtime.onInstalled.addListener((details) => {
     if (details.reason === 'install' || details.reason === 'update') {
         initUninstallURL();
+        purgeLegacySyncKeys();
     }
 });
 
 chrome.runtime.onStartup.addListener(() => {
     initUninstallURL();
+    purgeLegacySyncKeys();
 });
 
 // --- State Management ---
@@ -286,29 +288,14 @@ async function getPeerId() {
 }
 
 async function getSettings() {
-    // Try local (per-device) first, fall back to sync for migration
-    let data = await chrome.storage.local.get(['serverUrl', 'useCustomServer', 'roomId', 'password', 'username']);
-    let migrated = false;
-    if (!data.username) {
-        const syncData = await chrome.storage.sync.get(['serverUrl', 'useCustomServer', 'roomId', 'password', 'username']);
-        if (syncData.username || syncData.roomId) {
-            data = syncData;
-            migrated = true;
-        }
-    }
+    // Local-only by design. Room credentials (roomId/password) and identity
+    // (username) must NEVER come from storage.sync — syncing them across devices
+    // both leaks them and resurrects dead rooms on reinstall (a fresh install
+    // has empty local storage but sync survives in the user's Google account).
+    const data = await chrome.storage.local.get(['serverUrl', 'useCustomServer', 'roomId', 'password', 'username']);
     let username = data.username;
     if (!username) {
         username = generateUsername();
-    }
-    if (migrated) {
-        await chrome.storage.local.set({ 
-            serverUrl: data.serverUrl || '',
-            useCustomServer: data.useCustomServer || false,
-            roomId: data.roomId || '',
-            password: data.password || '',
-            username
-        });
-    } else if (!data.username) {
         await chrome.storage.local.set({ username });
     }
     return {
@@ -320,6 +307,19 @@ async function getSettings() {
     };
 }
 
+// Privacy + correctness: only onboardingComplete and dismissedHints belong in
+// storage.sync. Everything else is per-device local storage. This actively
+// removes legacy keys that older versions wrote to sync (and that would
+// otherwise be redistributed across devices and resurrected on reinstall).
+const LEGACY_SYNC_KEYS = [
+    'serverUrl', 'useCustomServer', 'roomId', 'password', 'username',
+    'filterNoise', 'autoSyncNextEpisode', 'forceSyncMode',
+    'browserNotifications', 'autoCopyInvite', 'locale', 'audioSettings'
+];
+function purgeLegacySyncKeys() {
+    chrome.storage.sync.remove(LEGACY_SYNC_KEYS).catch(() => {});
+}
+
 function addLog(message, type = 'info') {
     const log = {
         timestamp: new Date().toISOString(),
@@ -1494,14 +1494,8 @@ function resetAudioProcessingInTab(tabId) {
 
 async function applyAudioSettingsToTab(tabId) {
     if (!tabId) return;
-    let data = (await chrome.storage.local.get(['audioSettings']));
-    if (!data.audioSettings) {
-        const syncData = await chrome.storage.sync.get(['audioSettings']);
-        if (syncData.audioSettings) {
-            data = syncData;
-            await chrome.storage.local.set({ audioSettings: syncData.audioSettings });
-        }
-    }
+    // Local-only: audioSettings are never read from storage.sync.
+    const data = await chrome.storage.local.get(['audioSettings']);
     chrome.tabs.sendMessage(tabId, {
         action: 'APPLY_AUDIO_SETTINGS',
         settings: data.audioSettings
diff --git a/extension/content.js b/extension/content.js
index e53e488..aa6458f 100644
--- a/extension/content.js
+++ b/extension/content.js
@@ -89,25 +89,8 @@
     let _audioSettings = null;
     let _audioProcessingAllowed = true;
 
-    // Cache the autoSyncNextEpisode setting
+    // Cache the autoSyncNextEpisode setting (local-only; never read from sync)
     chrome.storage.local.get(['autoSyncNextEpisode', 'audioSettings'], (data) => {
-        if (data.autoSyncNextEpisode === undefined || data.audioSettings === undefined) {
-            chrome.storage.sync.get(['autoSyncNextEpisode', 'audioSettings'], (syncData) => {
-                const migrate = {};
-                if (data.autoSyncNextEpisode === undefined && syncData.autoSyncNextEpisode !== undefined) {
-                    migrate.autoSyncNextEpisode = syncData.autoSyncNextEpisode;
-                }
-                if (data.audioSettings === undefined && syncData.audioSettings !== undefined) {
-                    migrate.audioSettings = syncData.audioSettings;
-                }
-                if (Object.keys(migrate).length) chrome.storage.local.set(migrate);
-                _autoSyncEnabled = syncData.autoSyncNextEpisode !== false;
-                _audioSettings = mergeAudioSettings(syncData.audioSettings);
-                const v = findVideo();
-                if (v && _audioProcessingAllowed) applyAudioSettings(v, _audioSettings);
-            });
-            return;
-        }
         _autoSyncEnabled = data.autoSyncNextEpisode !== false;
         _audioSettings = mergeAudioSettings(data.audioSettings);
         const video = findVideo();
diff --git a/extension/popup.js b/extension/popup.js
index 764ddf1..5f5467f 100644
--- a/extension/popup.js
+++ b/extension/popup.js
@@ -175,19 +175,9 @@ function setRoomRefreshCooldown() {
 
 // --- Initialization ---
 async function init() {
+    // Local-only by design — settings and room credentials never come from
+    // storage.sync (only onboardingComplete + dismissedHints live there).
     const localData = await chrome.storage.local.get(['serverUrl', 'useCustomServer', 'roomId', 'password', 'username', 'filterNoise', 'autoSyncNextEpisode', 'forceSyncMode', 'browserNotifications', 'autoCopyInvite', 'locale', 'audioSettings', 'activeTab']);
-    // Migrate preferences from sync → local for existing users
-    const oldSync = await chrome.storage.sync.get(['serverUrl', 'useCustomServer', 'roomId', 'password', 'username', 'filterNoise', 'autoSyncNextEpisode', 'forceSyncMode', 'browserNotifications', 'autoCopyInvite', 'locale', 'audioSettings']);
-    const toMigrate = {};
-    for (const key of ['serverUrl', 'useCustomServer', 'roomId', 'password', 'username', 'filterNoise', 'autoSyncNextEpisode', 'forceSyncMode', 'browserNotifications', 'autoCopyInvite', 'locale', 'audioSettings']) {
-        if (localData[key] === undefined && oldSync[key] !== undefined) {
-            toMigrate[key] = oldSync[key];
-            localData[key] = oldSync[key];
-        }
-    }
-    if (Object.keys(toMigrate).length) {
-        await chrome.storage.local.set(toMigrate);
-    }
 
     let activeLang = localData.locale;
     if (!activeLang) {