I am to lazy to dig it up and link the PDF, but there was a whitepaper about the Volkswagen keyfobs. In terms of modulation it's unsurprisingly simple, on-off keying, nothing wrong with that. In terms of data transmitted they have several encrypted protocols/versions, but they all suffer from the same implementation problem: there is only one encryption key used for the entire global fleet of cars. Imagine making something as brutally broken as that :D

Older systems that don't let the car interrogate the fob mitigate it as well as long as you have mutiple encryption keys. Looking at you vw.