Android : Android Detect Pressing On Power Key

My Application needs to know if the screen went off due to timeout or the user clicked the power button.

I decided to check if the power button was pressed. I read some Q&A here and came up with this :

public class MyActivity extends Activity {    

    /**
     * Called when the activity is first created.
     */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if (keyCode == KeyEvent.KEYCODE_POWER) {
            Log.w("Test", "Power button down detected");
            return true;
        }
        return false;
    }


    @Override
    public boolean onKeyUp(int keyCode, KeyEvent event) {
        if (keyCode == KeyEvent.KEYCODE_POWER) {
            Log.w("Test", "Power button up detected");
        }
        return false;
    }
}

I also added this:

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

This doesn't work, it doesn't print the log.