The best anti-theft devices (that'll get you sued):
Built-in nuke with self destruct sequence (you probably don't want to be around).
1,000 underbody razor blades and motion sensing chainsaw (tipping problem solved).
Flamethrowers attached to tow hooks (might stick out a little)
Motion sensing automatic machine gun (run if you can)
High Voltage door handles (try to get in now!).
Net shooter (to catch those bad guys).
Missile pods (you don't want them to get away).
Acid shooter (what happens if the machine gun, the flamethrower, missiles, or net doesn't get them? Acid will).
Did I leave out any illegal devices?