I would have a bluetooth or RF dongle on my keychain. When in range, this dongle would talk to the PIC box.
The PIC box has a microcontroller and some way to read the signal the dongle is sending out.
When the dongle is in range of the PIC box, the box picks up on the signal of the dongle. When the signal is picked up, the box unlocks the door(s), activates the relay for the engine button, and boots/unhybernates the carputer.
The dongle might also have a few buttons to perhapse control windows, trunk pop, and/or siren.