DeviceWatcher Class


Enumerates devices dynamically, so that the app receives notifications if devices are added, removed, or changed after the initial enumeration is complete.

public ref class DeviceWatcher sealed
class DeviceWatcher sealed
[Windows.Foundation.Metadata.ContractVersion(typeof(Windows.Foundation.UniversalApiContract), 65536)]
public sealed class DeviceWatcher
Public NotInheritable Class DeviceWatcher

Windows 10 requirements

Device family
Windows 10 (introduced in 10.0.10240.0)
API contract
Windows.Foundation.UniversalApiContract (introduced in v1.0)


For complete implementations in C#, C++, and JavaScript, see the Device enumeration and pairing sample.

This example incrementally enumerates devices, adding them to a list each time a device is found, and also handling removals and updates. The onAdded function that handles the added event takes a DeviceInformation object. Once enumeration is complete, the app prints a list of devices. The app also prints a message if devices are added, updated, or removed after the initial enumeration completes.

<!DOCTYPE html>
    <title>Device Enumeration Sample</title>
    var watcher;
    var deviceArray = new Array(); // Saves the enumeration results.

    function WatchDevices() {
        try {
            output.innerHTML = ""; // Clears output field.

            watcher = 
            // Add event handlers
            watcher.addEventListener("added", onAdded);
            watcher.addEventListener("removed", onRemoved);
            watcher.addEventListener("updated", onUpdated);
            watcher.addEventListener("stopped", onStopped);
            // Start enumerating and listening for events
        } catch (e) {
            document.getElementById("statusMessage").innerHTML = 
                "Failed to create watcher, error: " + e.message;

    function stopWatcher() {
        try {
        catch (e) {
            document.getElementById("statusMessage").innerHTML = 
                "Failed to stop watcher: " + e.message;

    function onAdded(devinfo) {
        document.getElementById("output").innerHTML += "<p>Device added: " + 
   + "</p>";

    function onUpdated(devUpdate) {
        document.getElementById("output").innerHTML += "<p>Device updated.</p>";
        for (var i = 0; i < deviceArray.length; i++) {
            if (deviceArray[i].id == {

    function onRemoved(devupdate) {
        document.getElementById("output").innerHTML += "<p>Device removed.</p>";
        for (var i = 0; i < deviceArray.length; i++) {
            if (deviceArray[i].id == {

    function onEnumerationCompleted(obj) {
        document.getElementById("output").innerHTML += 
            "<p>Enumeration Completed.</p>";

    function onStopped(obj) {
        document.getElementById("output").innerHTML += "<p>Stopped.</p>";

    // Prints the friendly name of the device interface, 
    // its ID (device interface path), and whether it is enabled.
    function printDevice(deviceInterface, outputDestination) {
        outputDestination.innerHTML += "<p>Name: " + 
   + "<p/>"; 
        outputDestination.innerHTML += "<p>Interface ID: " + 
   + "<p/>";    
        outputDestination.innerHTML += "<p>Enabled: " + 
            deviceInterface.isEnabled + "<p/>";
        outputDestination.innerHTML += "<br/>";

    function printDeviceArray(outputDestination) {
        for (var i = 0; i < deviceArray.length; i++) {
            printDevice(deviceArray[i], outputDestination);

<body role="application">
    <h1>Device Enumeration Sample</h1>
        <p>This example incrementally enumerates devices, adding them to a list each time a device is found, and also watching for
            updates. After enumeration is complete, the list of devices is printed.</p> 
            <input type="button" value="Watch(All Devices)" onclick="WatchDevices()"/>

            <input type="button" value="Stop" onclick="stopWatcher()"/>

        <div id="statusMessage"></div>
        <!--  Output -->
        <div  id="output"></div>


An app calls Start to begin the search for devices. During this initial enumeration, the DeviceWatcher raises an Added event for each device that's found, until all devices are found. The DeviceWatcher raises an EnumerationCompleted event when the initial enumeration is complete, and continues to raise events if a device is added, updated, or removed.

The following diagram shows how the DeviceWatcher transitions between the states represented by DeviceWatcherStatus enumeration.

state diagram of DeviceWatcher states

The Start method can only be called when the DeviceWatcher is in the Created, Stopped or Aborted state. The Status property indicates the DeviceWatcher state. When re-starting the watcher, wait for the Stopped event before calling Start.

Stop transitions the DeviceWatcher to the Stopping state and completes immediately. The watcher will transition to the Stopped state once all events that are already in the process of being raised have completed.

Apps may wait for the Stopped event if they need to know when the DeviceWatcher has stopped. Callers must wait for the Stopped event before they can call Start to restart the watcher. Callers may unsubscribe from events if they do not want to receive any additional events after Stop but do not want to wait for the Stopped event.


An app must subscribe to all of the added, removed, and updated events to be notified when there are device additions, removals or updates. If an app handles only the added event, it will not receive an update if a device is added to the system after the initial device enumeration completes.



The status of the DeviceWatcher.



Gets a DeviceWatcherTrigger object monitoring for changes to the list of devices.


Starts a search for devices, and subscribes to device enumeration events.


Stop raising the events that add, update and remove enumeration results.



Event that is raised when a device is added to the collection enumerated by the DeviceWatcher.


Event that is raised when the enumeration of devices completes.


Event that is raised when a device is removed from the collection of enumerated devices.


Event that is raised when the enumeration operation has been stopped.


Event that is raised when a device is updated in the collection of enumerated devices.

Applies to

See also