"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
"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..."
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