And how that will protect you from repeater attack? I just steal your car while you are in mall with this just as easy, encryption or not. I don't care about the signal, just that I capture it, send it to my other device near your car and kaboom!, your car unlocked.
The key fob would always return a response the exact same amount of time after receiving the challenge, so couldn't the car learn the distance by measuring the time of flight?
