diff --git a/js/modules/signal.js b/js/modules/signal.js
index 24513205e270..164af85aef55 100644
--- a/js/modules/signal.js
+++ b/js/modules/signal.js
@@ -131,7 +131,6 @@ const { QualifiedAddress } = require('../../ts/types/QualifiedAddress');
 const Initialization = require('./views/initialization');
 
 // Workflow
-const { IdleDetector } = require('./idle_detector');
 const MessageDataMigrator = require('./messages_data_migrator');
 
 // Processes / Services
@@ -413,7 +412,6 @@ exports.setup = (options = {}) => {
   };
 
   const Workflow = {
-    IdleDetector,
     MessageDataMigrator,
   };
 
diff --git a/js/modules/idle_detector.js b/ts/IdleDetector.ts
similarity index 50%
rename from js/modules/idle_detector.js
rename to ts/IdleDetector.ts
index a012271cbd35..2a5d74344a7f 100644
--- a/js/modules/idle_detector.js
+++ b/ts/IdleDetector.ts
@@ -1,54 +1,50 @@
-// Copyright 2018-2020 Signal Messenger, LLC
+// Copyright 2018-2021 Signal Messenger, LLC
 // SPDX-License-Identifier: AGPL-3.0-only
 
-/* eslint-env browser */
-
-const EventEmitter = require('events');
+import EventEmitter from 'events';
+import * as log from './logging/log';
 
 const POLL_INTERVAL_MS = 5 * 1000;
 const IDLE_THRESHOLD_MS = 20;
 
-class IdleDetector extends EventEmitter {
-  constructor() {
-    super();
-    this.handle = null;
-    this.timeoutId = null;
+export class IdleDetector extends EventEmitter {
+  private handle: undefined | ReturnType<typeof requestIdleCallback>;
+  private timeoutId: undefined | ReturnType<typeof setTimeout>;
+
+  public start(): void {
+    log.info('Start idle detector');
+    this.scheduleNextCallback();
   }
 
-  start() {
-    window.SignalContext.log.info('Start idle detector');
-    this._scheduleNextCallback();
-  }
-
-  stop() {
+  public stop(): void {
     if (!this.handle) {
       return;
     }
 
-    window.SignalContext.log.info('Stop idle detector');
-    this._clearScheduledCallbacks();
+    log.info('Stop idle detector');
+    this.clearScheduledCallbacks();
   }
 
-  _clearScheduledCallbacks() {
+  private clearScheduledCallbacks() {
     if (this.handle) {
       cancelIdleCallback(this.handle);
-      this.handle = null;
+      delete this.handle;
     }
 
     if (this.timeoutId) {
       clearTimeout(this.timeoutId);
-      this.timeoutId = null;
+      delete this.timeoutId;
     }
   }
 
-  _scheduleNextCallback() {
-    this._clearScheduledCallbacks();
+  private scheduleNextCallback() {
+    this.clearScheduledCallbacks();
     this.handle = window.requestIdleCallback(deadline => {
       const { didTimeout } = deadline;
       const timeRemaining = deadline.timeRemaining();
       const isIdle = timeRemaining >= IDLE_THRESHOLD_MS;
       this.timeoutId = setTimeout(
-        () => this._scheduleNextCallback(),
+        () => this.scheduleNextCallback(),
         POLL_INTERVAL_MS
       );
       if (isIdle || didTimeout) {
@@ -57,7 +53,3 @@ class IdleDetector extends EventEmitter {
     });
   }
 }
-
-module.exports = {
-  IdleDetector,
-};
diff --git a/ts/background.ts b/ts/background.ts
index 5ff1af8653d3..073b921deced 100644
--- a/ts/background.ts
+++ b/ts/background.ts
@@ -37,6 +37,7 @@ import { dropNull } from './util/dropNull';
 import { normalizeUuid } from './util/normalizeUuid';
 import { filter } from './util/iterables';
 import { isNotNil } from './util/isNotNil';
+import { IdleDetector } from './IdleDetector';
 import { senderCertificateService } from './services/senderCertificate';
 import { GROUP_CREDENTIALS_KEY } from './services/groupCredentialFetcher';
 import * as KeyboardLayout from './services/keyboardLayout';
@@ -160,6 +161,8 @@ export async function cleanupSessionResets(): Promise<void> {
 }
 
 export async function startApp(): Promise<void> {
+  const idleDetector = new IdleDetector();
+
   await KeyboardLayout.initialize();
 
   window.Whisper.events = window._.clone(window.Backbone.Events);
@@ -436,7 +439,7 @@ export async function startApp(): Promise<void> {
   //   of preload.js processing
   window.setImmediate = window.nodeSetImmediate;
 
-  const { IdleDetector, MessageDataMigrator } = window.Signal.Workflow;
+  const { MessageDataMigrator } = window.Signal.Workflow;
   const { removeDatabase: removeIndexedDB, doesDatabaseExist } =
     window.Signal.IndexedDB;
   const { Message } = window.Signal.Types;
@@ -451,7 +454,6 @@ export async function startApp(): Promise<void> {
   log.info('background page reloaded');
   log.info('environment:', window.getEnvironment());
 
-  let idleDetector: WhatIsThis;
   let newVersion = false;
 
   window.document.title = window.getTitle();
@@ -585,9 +587,7 @@ export async function startApp(): Promise<void> {
 
         // Stop background processing
         AttachmentDownloads.stop();
-        if (idleDetector) {
-          idleDetector.stop();
-        }
+        idleDetector.stop();
 
         // Stop processing incoming messages
         if (messageReceiver) {
@@ -747,7 +747,6 @@ export async function startApp(): Promise<void> {
 
     Views.Initialization.setMessage(window.i18n('loading'));
 
-    idleDetector = new IdleDetector();
     let isMigrationWithIndexComplete = false;
     log.info(
       `Starting background data migration. Target version: ${Message.CURRENT_SCHEMA_VERSION}`
diff --git a/ts/window.d.ts b/ts/window.d.ts
index 7d75d6205481..78ff3321fc14 100644
--- a/ts/window.d.ts
+++ b/ts/window.d.ts
@@ -401,7 +401,6 @@ declare global {
       };
       OS: typeof OS;
       Workflow: {
-        IdleDetector: WhatIsThis;
         MessageDataMigrator: WhatIsThis;
       };
       IndexedDB: {