I've figured things out this way on my '08-if I lock the doors with the inside button or the key I can open them with the key OR the transmitter.If I lock them with the transmitter,I MUST open the doors with the transmitter or the alarm will sound off.

 

The key fobs are programmed to the BCM by the ID number of the fobs. And Snoopy is correct that these are random codes sent through RF.

 

Snopes has a lengthy discussion of this "scanner" business, and concludes it is an urban myth. For one, the technology has advanced beyond making that possible, as Chevy Mgr has noted.

For another, if someone decides to steal your ride, there are much easier low tech methods. If someone wants it badly enough, they will find a way, even if it means hauling the vehicle onto a rollback truck and leaving. (More likely if you own a Lamborghini, I'd suspect.)

I had one attempted theft of an old Chevy conversion van, where the crooks managed to ruin the ignition lock but got no farther. To compensate themselves, they swiped two winter jackets that were headed to the Goodwill store and a computer monitor that was broken and headed to the nearest dumpster.

Someone put a pry bar under the door handle of my '97 Grand Caravan in an attempt to boost it, but also failed. The cop who took the report chided me for having a Club lock lying on the floor unused. As he observed, it's not that you can't defeat the Club, it's that the average car thief will see it on the wheel and decide to move on to a car that's easier to boost.

Here in MD there is a public service announcement running on radio, where the state police commander says the vast majority of auto thefts are cars parked with the keys left in the ignition.