Make:

The new Macbook's aren't the only laptops you can knock, slap and bump to perform commands - "For the first time, you can hit your computer and get a meaningful response! Using Linux and the Hard Drive Active Protection System (HDAPS) kernel drivers, you can access the embedded accelerometers on Lenovo (formerly IBM) ThinkPads, then process the accelerometer data to read specific sequences of "knocking" events -- literally rapping on the laptop case with your knuckles -- and run commands based on those knocks. Double tap to lock the screen, and knock in your secret code to unlock. Tap the display lid once to move your mp3 player to the next track. The possibilities are endless." [via] - Link.