As for car remote entry systems, from what I’ve read a typical keyfob uses a 40-bit code, which presents over 1 trillion combinations. The car and keyfob are both synched to the same pseudorandom number generator, so only the next x expected codes (x usually = 256) will open the door. If you COULD capture traffic on the 300-400MHz band (what the keyfob transmits in) you could get the freshly-expired codes, but I also wouldn’t know how difficult it would be to deduce the PRN algo from what you got. You’d probably need to capture a hell of a lot of traffic from the exact same car, in which case you’re probably better off just walking up and smashing the windows.