Oh good. Now you can annoy your friend with a small gadget you can hide. Place it somewhere tough to locate and it produces one of three annoying randomly occurring sounds.
Implications - The thin design helps makes it even tougher for your friends to find it due to its size. With the additional magnet, you can even hide it in a variety of places that people will least expect to find. There are three irritating frequencies to choose from, 2kHz, 12kHz or alternating, which will probably be the cause of a sane person's eventual descent into insanity.
The ThinkGeek Annoy-a-tron would make a great prank, but use it at your own risk as it may create a rampage with devastating results.