Modern cars already have a complex sequence to enter pairing mode.
You need to press buttons inside the car, buttons on the currently paired key (to prove possession of that) and buttons on the key you want to pair with.
So a passer by would have to press a button on their fob at just the right moment. Then when you go to test your new key fob, it wouldn't work, so you would pair again until it was your key that was paired.
You need to press buttons inside the car, buttons on the currently paired key (to prove possession of that) and buttons on the key you want to pair with.
So a passer by would have to press a button on their fob at just the right moment. Then when you go to test your new key fob, it wouldn't work, so you would pair again until it was your key that was paired.