I had a C7 that was stolen. It probably took the thief 5 minutes. Broke the window, alarm went off but they put a device in the ODB, reprogrammed the computer and drove away.

I have a new C8 now and would like to know what anyone may be using to keep the car ignition system from being fooled into thinking the cars real remote control is being used.

 

Congratulations on obtaining a C-8, I myself haven't made that move yet. You have many options you can use but there is no sure way to not have the car stolen. There is the flat bed tow truck where they slide it up on the truck and it's gone. If the onstar is active it can be traced until its deactivated. There is the option of adding a second alarm where the car won't start and it makes noise, or you can add mechanical switches that you turn off when leaving the car that can deactivate the ignition and or the fuel pump or both. That would keep them from driving away. They won't take the time to trouble shoot the problem. Bought a used c-3 years back that someone had a Clifford system installed on it addition to stock beeping horn so now it makes more noise and the lights flash. I do have a manual switch that disconnects the ignition. Clifford I think also has the ability to disengage the ignition. I heard of a Viper alarm system, I know nothing about. I'm sure there are other systems out there that can be used along with your stock system, that would keep someone from driving away.

 

Welcome to the forum. My dealer made me put LoJack on my new C8 as part of a package. While it won't stop them from getting it, it will locate it for you even if they disable OnStar.
If you don't plan on driving it everyday, it's highly recommended that you use a battery maintainer. These cars have a lot of electronics that don't completely go to sleep when the car is off and will drain the battery in fairly short order. I didn't drive it for about a week and it didn't have enough power to unlock the doors. It did have enough power to start it however. I suspect that it has a built-in shut down for the battery so if gets so low, it doesn't go completely flat. Great car however.