There were already 2 options listed here. They are both valid depending on your use case. I’s like to add a 3rd option however incomplete.

Option 1 : find connected nodes using NodeApi

The NodeApi class has a method for retrieving connected nodes. With this you’re sure that the user didn’t just had a watch in the past or tested one sometime. He really has a watch nearby and connected.

Drawback of this approach is that you will get no results if bluetooth is not enabled or the watch is not connected at the moment.

The method is:

List<Node> connectedNodes =
Wearable.NodeApi.getConnectedNodes(mGoogleApiClient).await().getNodes();

A more complete code example looks like this:

private GoogleApiClient client;
private static final long CONNECTION_TIME_OUT_MS = 1000;

public void checkIfWearableConnected() {

    retrieveDeviceNode(new Callback() {
        @Override
        public void success(String nodeId) {
            Toast.makeText(this, "There was at least one wearable found", Toast.LENGTH_SHORT).show();
        }

        @Override
        public void failed(String message) {
            Toast.makeText(this, "There are no wearables found", Toast.LENGTH_SHORT).show();
        }
    });

}

private GoogleApiClient getGoogleApiClient(Context context) {
        if (client == null)
            client = new GoogleApiClient.Builder(context)
                    .addApi(Wearable.API)
                    .build();
        return client;
    }

private interface Callback {
        public void success(final String nodeId);
        public void failed(final String message);
    }

private void retrieveDeviceNode(final Callback callback) {
        final GoogleApiClient client = getGoogleApiClient(this);
        new Thread(new Runnable() {

            @Override
            public void run() {
                client.blockingConnect(CONNECTION_TIME_OUT_MS, TimeUnit.MILLISECONDS);
                NodeApi.GetConnectedNodesResult result =
                        Wearable.NodeApi.getConnectedNodes(client).await();
                List<Node> nodes = result.getNodes();
                if (nodes.size() > 0) {
                    String nodeId = nodes.get(0).getId();
                    callback.success(nodeId);
                } else {
                    callback.failed("no wearables found");
                }
                client.disconnect();
            }
        }).start();
    }

Option 2 : check for the Android Wear App

And that is the advantage of the second option. If you get a watch the first thing you to do to get it connected is to install the Android Wear app on your handheld. So you can use the PackageManager to verify if this Android Wear app is installed.

Drawback here is that you could get the wear app installed without having a watch.

Code example:

try {
    getPackageManager().getPackageInfo("com.google.android.wearable.app", PackageManager.GET_META_DATA);

    Toast.makeText(this, "The Android Wear App is installed", Toast.LENGTH_SHORT).show();
} catch (PackageManager.NameNotFoundException e) {
    //android wear app is not installed
    Toast.makeText(this, "The Android Wear App is NOT installed", Toast.LENGTH_SHORT).show();
}

Option 3 : Check for paired devices

Not sure if this is possible but in some cases this would be the perfect solution since you can check that the user has a watch paired with his device while it doesn’t has to be connected at the time.

Below is a code example, however this doesn’t include checking if the paired devices are wearables or not. This is only a starting point.

Code example from: getbondeddevices() not returning paired bluetooth devices

BluetoothAdapter mBtAdapter = BluetoothAdapter.getDefaultAdapter();

Set<BluetoothDevice> pairedDevices = mBtAdapter.getBondedDevices();
if (pairedDevices.size() > 0) {
     Toast.makeText(this, "At least one paired bluetooth device found", Toast.LENGTH_SHORT).show();
    // TODO at this point you'd have to iterate these devices and check if any of them is a wearable (HOW?)
    for (BluetoothDevice device : pairedDevices) {
        Log.d("YOUR_TAG", "Paired device: "+ device.getName() + ", with address: " + device.getAddress());
    }
} else {
    Toast.makeText(this, "No paired bluetooth devices found", Toast.LENGTH_SHORT).show();
}

Note that this code requires bluetooth permissions in your manifest.

<uses-permission android:name="android.permission.BLUETOOTH" />
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN"/>