***

id: c25990e6-9800-4ea1-b5b1-fe7f0b29e02f
title: createDeviceWatcher
slug: /js/reference/webrtc/create-device-watcher
description: createDeviceWatcher function in the WebRTC namespace.
max-toc-depth: 3
----------------

### createDeviceWatcher

* `Const` **createDeviceWatcher**(`options?`): `Promise<EventEmitter<DeviceWatcherEvents, any>>`

Asynchronously returns an event emitter that notifies changes in the devices. The possible events are:

* `"added"`: A device has been added.
* `"removed"`: A device has been removed.
* `"updated"`: A device has been updated.
* `"changed"`: Any of the previous events occurred.

In all cases, your event handler gets as parameter an object `e` with the following keys:

* `e.changes`: The changed devices. For `"added"`, `"removed"`, and `"updated"` event handlers, you only get the object associated to the respective event (i.e., only a list of added devices, removed devices, or updated devices). For `"changed"` event handlers, you get all three lists.
* `e.devices`: The new list of devices.

For device-specific helpers, see [createCameraDeviceWatcher](/docs/browser-sdk/v3/js/reference/webrtc/create-camera-device-watcher), [createMicrophoneDeviceWatcher](/docs/browser-sdk/v3/js/reference/webrtc/create-microphone-device-watcher), and [createSpeakerDeviceWatcher](/docs/browser-sdk/v3/js/reference/webrtc/create-speaker-device-watcher).

#### Parameters

<ParamField path="options" type="CreateDeviceWatcherOptions">
  If omitted, the event emitter is associated to all devices for which we have permission. Otherwise, pass an object `{ targets: string[] }`, where `targets` is a list of categories. Allowed categories are `"camera"`, `"microphone"`, and `"speaker"`.
</ParamField>

#### Returns

`Promise<EventEmitter<DeviceWatcherEvents, any>>`

#### Examples

Creating an event listener on the `"changed"` event:

```javascript
await SignalWire.WebRTC.getUserMedia({ audio: true, video: false });
h = await SignalWire.WebRTC.createDeviceWatcher();
h.on("changed", (c) => console.log(c));
```

Getting notified only for audio input and output devices:

```javascript
h = await SignalWire.WebRTC.createDeviceWatcher({
  targets: ["microphone", "speaker"],
});
h.on("changed", (c) => console.log(c));
```