Listening to Sensors using SensorManager

Overview

Different devices have a variety of sensors that can be accessed via the Sensor framework. Possible tasks related to sensors include:

• List available sensors
• Determine sensor capabilities (range, resolution, etc)
• Acquire raw sensor data
• Register sensor event listeners

Sensor Types

Common sensors that devices have available are for temperature, light, pressure, acceleration, motion, and orientation. Here's a list of guides:

• Motion Sensors
• Position Sensors
• Environment Sensors

See the full list of sensors for more details.

Listening to Sensors

You can register for sensor events:

private SensorManager mSensorManager;
private Sensor mLight;

private SensorEventListener mLightSensorListener = new SensorEventListener() {
	@Override
	public void onSensorChanged(SensorEvent event) {
		Log.d("MY_APP", event.toString());
	}

	@Override
	public void onAccuracyChanged(Sensor sensor, int accuracy) {
		Log.d("MY_APP", sensor.toString() + " - " + accuracy);
	}
};

@Override
protected void onCreate(Bundle savedInstanceState) {
	super.onCreate(savedInstanceState);
	setContentView(R.layout.activity_sensor);
	// Get sensor manager
	mSensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
	// Get the default sensor of specified type
	mLight = mSensorManager.getDefaultSensor(Sensor.TYPE_LIGHT);
}

@Override
protected void onResume() {
	super.onResume();
	if (mLight != null) {
	  mSensorManager.registerListener(mLightSensorListener, mLight, 
             SensorManager.SENSOR_DELAY_NORMAL);
	}
}

@Override
protected void onPause() {
  super.onPause();
  if (mLight != null) {
      mSensorManager.unregisterListener(mLightSensorListener);
  }
}

It's also important to note that this example uses the onResume() and onPause() callback methods to register and unregister the sensor event listener. As a best practice you should always disable sensors you don't need, especially when your activity is paused. Failing to do so can drain the battery in just a few hours because some sensors have substantial power requirements and can use up battery power quickly.

Require Sensors

If you are publishing your application on Google Play you can use the element in your manifest file to filter your application from devices that do not have the appropriate sensor configuration for your application.

<uses-feature android:name="android.hardware.sensor.accelerometer" android:required="true" />

If you add this element and descriptor to your application's manifest, users will see your application on Google Play only if their device has an accelerometer. You should set the descriptor to android:required="true" only if your application relies entirely on a specific sensor.

Sensors in the Background

In certain cases, an app wants to be listening to sensors in the background even while the app is not running. While this can be extremely draining to the battery if caution is not taken, this can be done with the use of a Service.

See this sensors in the background. To get sensor readings while the phone is asleep, we can implement a partial wake lock as described here. Here's working sample code for this as well.

References

• http://developer.android.com/guide/topics/sensors/sensors_overview.html