I have been using https://play.google.com/store/apps/details?id=com.sygel.goob... for about a year now and it has drastically increased my ability to get out of bed on time.

It works via wifi signal strength; I have to walk right up to my router in another room in order to shut it off (or you can reverse the trigger if you sleep near your router).

Across the room was never enough for me but walking to another room of the house wakes me up every time.