Sonick...look up schematics on a garage door opener. That should basically be what you're after. You might have to swap in FM for whatever garage doors use (not sure) but the principle is the same, right?
##EDIT##
I've also seen doorbells for houses that don't have wiring at the door. Transmitter is a thumb-sized box that you stick on the doorframe, receiver is a fist-sized box that you place somewhere in the foyer/entry hall...it receives the signal and initiates a chime. Schematics on that should also work.
##EDIT##
I've also seen doorbells for houses that don't have wiring at the door. Transmitter is a thumb-sized box that you stick on the doorframe, receiver is a fist-sized box that you place somewhere in the foyer/entry hall...it receives the signal and initiates a chime. Schematics on that should also work.