Lock or alarm suggestions

Either hide the car so they can't find it, take the key back from them or have it rekeyed. You could also buy a boot and boot the wheels when you park it.

Visit your local Chevrolet Dealer or a reputable locksmith. You'll need to have them go into the computer and remove all the programmed keys from the computer memory with a scan tool. Then they can reprogram your current key. I'd ask for a second key, for you, to be programmed to the vehicle as well. Always good to have a spare! If you have a key fob you'll need to have them do the same for the fob as well. Off the top of my head I'd say you're looking at about $200 to $300 to have this done. Also keep in mind that you can, on a GM, program additional keys yourself to the vehicle with only one working key. HOWEVER, this will NOT remove the second key, that's in the other person's hands from the vehicle's computer. In the meantime, remove the cover from the underhood fuse box and look for the fuel pump relay. When you park the vehicle, remove the relay and take it with you. This will cause the fuel pump not to work if the other person tries to steal the vehicle. The engine will run for about a minute or two then just die. It won't restart either until the relay is put back in! Hope that helps! Jim