[ Thanks to IdaAshley for this link.
]
“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…”