diff --git a/lib/app.jsx b/lib/app.jsx
index 8af19890d..3441d9618 100644
--- a/lib/app.jsx
+++ b/lib/app.jsx
@@ -517,7 +517,13 @@ export const App = connect(mapStateToProps, mapDispatchToProps)(
         throw new Error('Unknown dialog type.');
       }
 
-      return <DialogComponent {...this.props} {...{ key, dialog, params }} />;
+      return (
+        <DialogComponent
+          isElectron={isElectron()}
+          {...this.props}
+          {...{ key, dialog, params }}
+        />
+      );
     },
   })
 );
diff --git a/lib/dialogs/settings.jsx b/lib/dialogs/settings.jsx
index cb1c142a7..8bd654661 100644
--- a/lib/dialogs/settings.jsx
+++ b/lib/dialogs/settings.jsx
@@ -13,6 +13,7 @@ export const SettingsDialog = React.createClass({
   propTypes: {
     actions: PropTypes.object.isRequired,
     onSignOut: PropTypes.func.isRequired,
+    isElectron: PropTypes.bool.isRequired,
   },
 
   onDone() {
@@ -37,6 +38,72 @@ export const SettingsDialog = React.createClass({
     });
   },
 
+  onSignOutRequested() {
+    // Safety first! Check for any unsynced notes before signing out.
+    const { onSignOut, noteBucket } = this.props;
+    const { notes } = this.props.appState;
+    const { getVersion } = noteBucket;
+
+    noteBucket.hasLocalChanges((error, hasChanges) => {
+      if (hasChanges) {
+        this.showUnsyncedWarning();
+        return;
+      }
+
+      // Also check persisted store for any notes with version 0
+      const noteHasSynced = note =>
+        new Promise((resolve, reject) =>
+          getVersion(note.id, (e, v) => (e || v === 0 ? reject() : resolve()))
+        );
+
+      Promise.all(notes.map(noteHasSynced)).then(
+        () => onSignOut(), // All good, sign out now!
+        () => this.showUnsyncedWarning() // Show a warning to the user
+      );
+    });
+  },
+
+  showUnsyncedWarning() {
+    const { isElectron } = this.props;
+    isElectron ? this.showElectronWarningDialog() : this.showWebWarningDialog();
+  },
+
+  showElectronWarningDialog() {
+    const { onSignOut } = this.props;
+    const dialog = __non_webpack_require__('electron').remote.dialog; // eslint-disable-line no-undef
+    dialog.showMessageBox(
+      {
+        type: 'warning',
+        buttons: ['Delete Notes', 'Cancel', 'Visit Web App'],
+        title: 'Unsynced Notes Detected',
+        message:
+          'Logging out will delete any unsynced notes. You can verify your ' +
+          'synced notes by logging in to the Web App.',
+      },
+      response => {
+        if (response === 0) {
+          onSignOut();
+        } else if (response === 2) {
+          viewExternalUrl('https://app.simplenote.com');
+        }
+      }
+    );
+  },
+
+  showWebWarningDialog() {
+    const { onSignOut } = this.props;
+    const shouldReallySignOut = confirm(
+      'Warning: Unsynced notes were detected.\n\n' +
+        'Logging out will delete any notes that have not synced. ' +
+        'Check your connection and visit app.simplenote.com to verify synced notes.' +
+        '\n\nClick OK to delete unsynced notes and Log Out.'
+    );
+
+    if (shouldReallySignOut) {
+      onSignOut();
+    }
+  },
+
   render() {
     var dialog = this.props.dialog;
 
@@ -91,7 +158,7 @@ export const SettingsDialog = React.createClass({
                 <button
                   type="button"
                   className="button button-primary"
-                  onClick={this.props.onSignOut}
+                  onClick={this.onSignOutRequested}
                 >
                   Log Out
                 </button>
diff --git a/package.json b/package.json
index be4c090e0..c3e4e0bfa 100644
--- a/package.json
+++ b/package.json
@@ -14,19 +14,19 @@
     "build": "NODE_ENV=development npm run build:dll && npm run build:app",
     "build:app": "webpack --config ./webpack.config.js",
     "build:dll": "webpack --config ./webpack.config.dll.js",
-    "build:prod":
-      "NODE_ENV=production webpack -p --config ./webpack.config.dll.js && webpack -p --config ./webpack.config.js",
+    "build:prod": "NODE_ENV=production webpack -p --config ./webpack.config.dll.js && webpack -p --config ./webpack.config.js",
     "format": "prettier --write {desktop,lib,sass}/{**/,*}.{js,json,jsx,sass}",
     "lint": "eslint --ext .js --ext .jsx lib",
-    "start":
-      "NODE_ENV=hot npm run build && webpack-dev-server --config ./webpack.config.js --content-base dist --host 0.0.0.0 --port 4000 --hot --inline"
+    "start": "NODE_ENV=hot npm run build && webpack-dev-server --config ./webpack.config.js --content-base dist --host 0.0.0.0 --port 4000 --hot --inline"
   },
   "license": "ISC",
   "engines": {
     "node": "7.9.0",
     "npm": "4.2.0"
   },
-  "browserslist": ["Chrome >= 58"],
+  "browserslist": [
+    "Chrome >= 58"
+  ],
   "jest": {
     "rootDir": "lib",
     "testRegex": "(/test/.*\\.jsx?)|(test\\.jsx?)$"
@@ -99,7 +99,7 @@
     "serve-favicon": "2.4.3",
     "showdown": "1.7.2",
     "showdown-xss-filter": "0.2.0",
-    "simperium": "0.2.9"
+    "simperium": "0.3.1"
   },
   "optionalDependencies": {
     "appdmg": "0.4.5"