Cesare's system uses key fob data to spoof a car's unlock signal, according to Wired. It's done using a tool called software-defined radio to broadcast at the necessary frequency and try several attempts per second until the doors open up. Once complete, he says that the only sign of tampering is that the owner's remote takes a few presses to work again.
If you're paranoid about thieves rolling down your block unlocking everything they see, don't be. Cesare's hack leans more towards an experiment than a realistic tool. While it only takes a few minutes in the video, that isn't a guarantee. The correct code changes each time, and it could take up to two hours to work, according to Wired. A traditional thief could have a car in another state by that time. Also, the hacker needs a portion of the unlock code to get started, and that requires capturing at least one command from the key fob. Finally, Cesare has only tested this on his own vehicle so far. He built a robot to press the button multiple times to capture the possible codes.
Thankfully, Cesare says he has no plans to make his code available to the public and is working to alert to manufacturer. Scroll down to see the hack and the robot in action.