Since we listen to the radio in the car while we drive, been doing that for years, that pretty much proves it is possible to transmit a radio signal from outside the car and receiving it inside. And after the reception of the radio signal, it's also pretty clear that could electronically initiate the unlocking of the door. That's how a garage door opener works. What isn't quite so obvious is how it is possible to insure only the owner's fob can unlock the door, and how to prevent someone with a radio receiver listening in from decoding the owner's fob signal and then using that knowledge to open the door themselves. And steal all the owner's Snickers bars.
OP might search on something like "one way encryption mapping", "pseudo random sequences", etc.