Contact microphones turn vibrations into electrical signals, and can then be transcoded into sound waves. This is precisely what the Mogees project does, and it does it well. The gadget can stick to any surface and turn it into your musical playground. There are multiple settings to help produce one's desired sound, but the real key resides in the gestures.
Using gestures is where the more unique sounds are discovered, and from the clip below they work flawlessly. Sliding, scratching, tapping and countless other gestures make this little device desirable for anyone. And to be honest, it would make quite an impression in public.
If you were hoping to slip one of these gadgets under your teacher's desk at school, then you might want to think up another prank - because the Mogees project isn't commercially available. Though, I know a number of people that would pay good money for a little device like this, so we could see a similar product on the market in due time. Until then, you'll just have to stick to playing music the old fashioned way - on your instruments.