Shake-To-Undo On A MacBook Pro

Paul Horowitz at OS X Daily writes:

The tiny app works by activating Command+Z when movement is detected by the SMS.

If you’re concerned about accidental undos from moving your Mac laptop around, you can prevent this by enabling the ‘Confirmation Overlay’ from Shake To Undo.app’s menubar.

This is basically useless unless you’re really into shaking your MacBook while writing, but the technology behind it is what intrigues me. I first learned about Sudden Motion Sensors (SMS) last year, when I opened my MacBook Pro to install a brand new SSD, and had done a bit of research online before replacing my hard drive. It turns out, this sensor was first implemented by Apple in a refreshed PowerBook line in 2005, and later in the July 2005 iBook. Since then, every portable Mac came with a Sudden Motion Sensor, albeit with differences between G4 laptops and Intel MacBooks.

The SMS acts as a security measure for the spinning hard drive. By calculating sudden acceleration in real time through an accelerometer, the SMS can “predict” when a computer is about to drop off a surface or your lap, and thus tells the hard drive to disengage the drive’s heads from the platters. In theory, this should prevent data loss or at least make for less damages to the drive.

As you can imagine, a number of hacks have arisen around SMS – tilt-based games and utilities like Shake To Undo. If you want to try it out for yourself, you can download the app over at GitHub. I don’t recommend it (it’s bad for your hard drive), but it sounds so ridiculous it might just be fun to test for an afternoon.