Configuring a head tracker for your head-mounted display using your Android mobile phone

My goal is to encode a headtracker for my display mounted on my head using my Android phone. The movement is transferred to the movement of the mouse, which, in turn, is used inside computer games. I want to install my Android phone on the back of the tracker, so it will be fixed on the back of the head. The Y axis is up, the x axis is pointing to the right, when looking straight ahead, this means that when you look at my rear head, you see the display of the mobile phone.

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public void onSensorChanged(SensorEvent event)
{
  // alpha is calculated as t / (t + dT)
  // with t, the low-pass filter time-constant
  // and dT, the event delivery rate

  final float alpha = 0.8;

  gravity[0] = alpha * gravity[0] + (1 - alpha) * event.values[0];
  gravity[1] = alpha * gravity[1] + (1 - alpha) * event.values[1];
  gravity[2] = alpha * gravity[2] + (1 - alpha) * event.values[2];

  linear_acceleration[0] = event.values[0] - gravity[0];
  linear_acceleration[1] = event.values[1] - gravity[1];
  linear_acceleration[2] = event.values[2] - gravity[2];
}

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