I've always been a heavy sleeper, and to top it off, I'm deaf also (require two hearing aids; obviously out when sleeping).
I currently use an alarm clock that has a strobe light in it, and an optional vibrating pad. There is an alarm sounder as well, but I tend not to use it. Not because I won't hear it, but because it sounds like I'm stood next to a nuclear warning klaxon it's that loud!
Either way, the vibrating pillow pad and the strobe light makes me wake up, whether I want to or not. Still has that effect 10 years later!