I’ve gotten a lot of mileage out of the fact that my wife can scare me just by walking into the room and speaking to me if I’m not expecting her to… even if I’m well aware that she’s home at the time.

One of my best men at my wedding, being one of my closest friends and well aware of my neuroses, gave my wife a bell to carry around with her, and she has actually used it on occasion.  But it’s a lot of work to use it, and far more fun for her to just terrorize me instead, I’m sure… :-)