Android detect phone lock event

Alternatively you could do this:

@Override
protected void onPause()
{
    super.onPause();

    // If the screen is off then the device has been locked
    PowerManager powerManager = (PowerManager) getSystemService(POWER_SERVICE);
    boolean isScreenOn;
    if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT_WATCH) {
        isScreenOn = powerManager.isInteractive();
    } else {
        isScreenOn = powerManager.isScreenOn();
    }

    if (!isScreenOn) {

        // The screen has been locked 
        // do stuff...
    }
}