Android service controlled by power/volume button - repost

I need a android application that includes a background service that play a sound when the physical power button is pressed 3 times in a row in 2 seconds. ( a time window) A sound(beep or any notification) should be played only when the button sequence is pressed. If the button is pressed outside the time window, nothing should be done and the counting starts over. If the power button is hard to implement I can also compromise on volume button. The background service should always run, starting at boot and should work even if the screen is turned off and the device is in sleep. Full source code is required. I consider this project to be very simple challenge with no long-term value, please consider that while bidding.