[fj5gtx]

Adding a kill switch will help. Likely they aren't going to spend anytime trying to figure out what is going on. Thieves know what to do with the factory setup, they are practiced and well prepared for what GM provided. Anything off script will defeat them, they aren't going to spend time trying to figure out why they can't get the car started.

Thief might break your glass and rekey your car before they discover they can't take it. Might want to think about what you can do to deter before they start doing damage to steal it.