I once read an article somewhere (I *think* it's in RISKS Digest, but I can't find it atm) about a chap who discovered how few "differs" there were in the signals transmitted by radio keyfobs. He then knocked up a radio transmitter which sprayed out every possible combination in turn, and demonstrated it in the car park of a nearby supermarket .... The narrator said he could hear cars happily and repeatedly unlocking and relocking themselves all over the car park.

I remember it largely because the narrator used the expression "brute-forcing the keyspace", which tickled my inner nerd.