door-hacking?

I think doors nowadays are smarter with their security. One thing I
heard about is the control may have an embedded random number
generator. When you push the button, the door sends a number, then the
control has to give back the right number. This might be implimented in
some kind of frequency-switching protocol. With the amount of effort
put into cell phones, it probably would be no problem for someone to
develop come up with some low-power method.

--Alexander