diff --git a/package.json b/package.json
index fde8f80800..f83fd54daa 100644
--- a/package.json
+++ b/package.json
@@ -20,6 +20,7 @@
     "css-loader": "^0.28.7",
     "electron": "1.8.2",
     "electron-builder": "19.56.0",
+    "electron-rebuild": "1.7.3",
     "electron-reload": "1.2.2",
     "electron-store": "^1.3.0",
     "extract-text-webpack-plugin": "^3.0.1",
@@ -55,6 +56,7 @@
     "rxjs": "^5.5.6",
     "zone.js": "^0.8.19",
     "angular2-toaster": "4.0.2",
-    "angulartics2": "5.0.1"
+    "angulartics2": "5.0.1",
+    "desktop-idle": "1.1.1"
   }
 }
diff --git a/src/app/accounts/settings.component.ts b/src/app/accounts/settings.component.ts
index 5cbf17f2ee..a11e2bbeba 100644
--- a/src/app/accounts/settings.component.ts
+++ b/src/app/accounts/settings.component.ts
@@ -36,7 +36,7 @@ export class SettingsComponent implements OnInit {
             { name: i18nService.t('thirtyMinutes'), value: 30 },
             { name: i18nService.t('oneHour'), value: 60 },
             { name: i18nService.t('fourHours'), value: 240 },
-            // { name: i18nService.t('onIdle'), value: -4 },
+            { name: i18nService.t('onIdle'), value: -4 },
             { name: i18nService.t('onSleep'), value: -3 },
             // { name: i18nService.t('onLocked'), value: -2 },
             { name: i18nService.t('onRestart'), value: -1 },
diff --git a/src/main/menu.main.ts b/src/main/menu.main.ts
index 79d812fc49..dd0f45ed77 100644
--- a/src/main/menu.main.ts
+++ b/src/main/menu.main.ts
@@ -10,8 +10,8 @@ import {
 
 import { WindowMain } from './window.main';
 
-import { MessagingService } from 'jslib/abstractions/messaging.service';
 import { I18nService } from 'jslib/abstractions/i18n.service';
+import { MessagingService } from 'jslib/abstractions/messaging.service';
 
 export class MenuMain {
     constructor(private windowMain: WindowMain, private i18nService: I18nService,
diff --git a/src/main/powerMonitor.main.ts b/src/main/powerMonitor.main.ts
index 41698e761f..cd91980e17 100644
--- a/src/main/powerMonitor.main.ts
+++ b/src/main/powerMonitor.main.ts
@@ -5,20 +5,47 @@ import { ConstantsService } from 'jslib/services/constants.service';
 import { MessagingService } from 'jslib/abstractions/messaging.service';
 import { StorageService } from 'jslib/abstractions/storage.service';
 
+// tslint:disable-next-line
+const desktopIdle = require('desktop-idle');
+const IdleLockSeconds = 5 * 60; // 5 minutes
+const IdleCheckInterval = 30 * 1000; // 30 seconds
+
 export class PowerMonitorMain {
+    private idle: boolean = false;
+
     constructor(private storageService: StorageService, private messagingService: MessagingService) { }
 
     init() {
         // System sleep
         powerMonitor.on('suspend', async () => {
-            const lockOption = await this.storageService.get<number>(ConstantsService.lockOptionKey);
+            const lockOption = await this.getLockOption();
             if (lockOption === -3) {
                 this.messagingService.send('lockVault');
             }
         });
 
-        // TODO: System idle
+        // System idle
+        global.setInterval(async () => {
+            const idleSeconds: number = desktopIdle.getIdleTime();
+            const idle = idleSeconds >= IdleLockSeconds;
+            if (idle) {
+                if (this.idle) {
+                    return;
+                }
+
+                const lockOption = await this.getLockOption();
+                if (lockOption === -4) {
+                    this.messagingService.send('lockVault');
+                }
+            }
+
+            this.idle = idle;
+        }, IdleCheckInterval);
 
         // TODO: System locked
     }
+
+    private async getLockOption(): Promise<number> {
+        return await this.storageService.get<number>(ConstantsService.lockOptionKey);
+    }
 }