Regarding wireless doorbells and car remotes, we have just such a doorbell, with a choice of treble or bass chimes. Ours is set to treble, but from time to time the bass would blast out when no one was at the door. We eventually noted that it happened either just after our then next-door neighbour had driven her Audi A3 into her drive, or just before she drove it out. It seems that her remote was on the same frequency as the set of chimes we weren't using. Luckily our bell push didn't start her car.