Heart rate monitor on smart watch does not start in onCreate method

Question

I don't think I fully understand the code behind heart rate monitoring. I created my project and this is the code I used.

   protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        // Enables Always-on
        setAmbientEnabled();

        mMobvoiApiClient = new MobvoiApiClient.Builder(this)
                .addApi(Wearable.API)
                .addConnectionCallbacks(this)
                .addOnConnectionFailedListener(this)
                .build();

        mSensorManager =
                (SensorManager)getSystemService(SENSOR_SERVICE);
        mHeartRate = mSensorManager.getDefaultSensor(
                Sensor.TYPE_HEART_RATE);


    }

I connect to the client here and get the default sensor here, declare it as TYPE_HEART_RATE.

protected void onResume() {
    super.onResume();
    mSensorManager.registerListener(this, mHeartRate,
            SensorManager.SENSOR_DELAY_NORMAL);
}

In the onResume method I register the listener.

   public void onSensorChanged(SensorEvent sensorEvent) {

        Log.d("Test", "Got the heart rate (beats per minute) : " +
                String.valueOf(sensorEvent.values[0]));
    }

So this method will generate log everytime the sensor data changes right? Correct me please, if I am wrong.

My main question is what method should I call or what listener should I use listener to activate my heart rate sensor on my watch. I am obviously missing out on something important but can't figure out what. For start I just want to activate the heart rate monitor to start getting data from it.

Thank you for answering.

EDIT: I already had the uses permission in the AndroidManifest file.

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

EDIT 2:

I tried adding two button one to register the listener and one to unregister it. When I try to register it with the startMeasure() method the boolean always returns Sensor Status:: Sensor registered: no

 public void OnClickBtn(View v){
        startMeasure();
    }

    public void OnClickBtnStop (View v){
        stopMeasure();
    }


    private void startMeasure() {
        boolean sensorRegistered = mSensorManager.registerListener(this, mHeartRate, SensorManager.SENSOR_DELAY_FASTEST);
        Log.d("Sensor Status:", " Sensor registered: " + (sensorRegistered ? "yes" : "no"));
    }

    private void stopMeasure() {
        mSensorManager.unregisterListener(this);
    }

It is connected with my layout like this

    <Button
        android:id="@+id/utrip"
        android:layout_width="wrap_content"
        android:layout_height="30dp"
        android:layout_marginLeft="20dp"
        android:layout_marginTop="60dp"
        android:background="@color/blue"
        android:onClick="OnClickBtn"
        android:text="@string/start" />

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="20dp"
        android:layout_marginTop="100dp"
        android:background="@color/dark_red"
        android:text="@string/stop"
        android:onClick="OnClickBtnStop"/>

I also get this from logcat.

sphal namespace is not configured for this process.

I think this has to do something with the API. This occurs when I press the Stop Button.