Anti Thief devices.... what works

A few other things-

Don't post pictures on the internet that have your car parked in your driveway or in front of your house. If your car sits outside, put a cover on it. Not for the locals, but so when Google flies over, or drives by for the "street view", you can't see some shiny classic sitting in the driveway. Professionals and amateur thieves are both using the internet to research and target properties, houses, cars, etc.