Silent Alarm Clock, ideas?

Hey, I could have necroposted in some threads that asked this but didn't get a lot of info (Mark would have a seizure), but I'm looking for a way to build/buy a CHEAP silent alarm. I need suggestions.

I'm hoping I can get some small device with a capacitor that has the ability to set the shock level to wake me up this way, like a watch. The goal is <$20 and powerful, it's gotta be enough to be unpleasant to the max.

The reason why I need this is I'm making an attempt at polyphasic sleep and I feel that unless I really fear my alarm, I'll just sleep right though. The silent part is a must too since I need to be able to set it at all hours and not piss off anyone else in the house.

This will be useful for school in the spring as well.