If you're one of those sadistic people who loves to terrify their friends and family, check out the "Scary Tapping Peeper." This thing would probably make me jump out of my skin. Basically, it's a latex face that you suction cup to the outside of a window, ideally with the head just at the base of the sill. When motion is detected, it taps three times on the glass.

The only reason I don't own this already is because it's in the neighborhood of 50 bucks and I just don't know if it's worth it. There are cheaper peepers available that don't do the tapping, but are almost just as startling. You'll find several at this site.

If you happen to purchase or already own one of these, odds are you'll be getting some reactions on video. Please send me a link so I can check it out and share it, with your permission of course.