They imbed it with the main computer.
I found that all new GM cars have Onstar built in. When you license OnStar you are in effect only buying the User Interface. The Guts are in every car. They can actually call your car while driving un-benownst to you, find your location and listen to you conversations.
There is a company that sells a disabling unit. Buy Stock now.
I had a federal government employee tell me that. Even you don't buy onstar when you get a new GM car...It is there. And they can still activate it at will.