using a relay I basically made a switch to turn on and off the fuel pump, you can hide the switch anywhere in the car. One of my prefered installs is to wire it so the switch it uses is something like the AC button or something of the sort. You just need to be able to find the ground for the fuel pump. The downside to this is they can still tow the car but driving it away is impossible unless the switch is found. I have found some nice switchs using a reed switch and a magnet on your keychain to activate it. http://www.mr2.com/TEXT/IgnitionKillSwitch.html