best and cheapest idea ive had so far is a straight regular vibration alarm system and perhaps a baby watching cb device hidden under your seat opened every night with the other end in your bed room.. even though he opens your car and unplugs the alarm fast after it goes off cuz of whatever he does (open doors or hood or whatever) your gonna hear it straight in your ears and you have time to run out and kill him off with your shoe string after blinding him with your boxer shorts.
just a thought, you can probably choke him with your boxer shorts too...