I always liked the idea of a smoke grenade under the seat. If you fail to disarm the system, it sets off the smoke. Given that they are designed to be used in big open spaces, in the cab of a truck, you won't be able to see the steering wheel much less remove a stereo or hotwire the thing. Better make it orange so the local fire department doesn't try to fill it with water though. People may ignore alarms and blinking lights, but it is hard to miss the truck billowing orange smoke from the broken rear window, even if it is being towed away at the time!
-- Joe
-- Joseph M. Krzeszewski Mechanical Engineering and stuff snipped-for-privacy@wpi.edu Jack of All Trades, Master of None... Yet