"In 2003, IBM started selling ThinkPad laptop computers with integrated accelerometers and associated software for a commercial operating systems to protect the hard disks when the ThinkPad is dropped. Enterprising hackers from IBM and elsewhere have worked to develop modules for the Linux kernel to take advantage of these sensors. On-screen display orientation, desktop switching, even game control and real-time 3-D models of the tilt of the laptop are now available.
"In mid-2006, knock-based commands for Linux laptops became available with user-space Perl scripts (as opposed to C-based code buried in kernel space), allowing users to run arbitrary commands based on specific knock sequences..."
