Hmm.. all good ideas. I suppose to avoid being sued it would be good to ramp up the volume so that people have a chance to abandon ship before their eardrums break. I've already ruled out carving the word "thief" into their forehead with a laser as probably too drastic. Oh and the bear trap that snaps shut when you reach inside the dash would probably be a bit much too.

With a radar-equiped car alarm, the air horn could go off whenever there is movement inside the vehicle.

-Hoagy.