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Turn a MacBook's sudden motion sensor on/off

There once was a time when you only had to sneeze in a room that had a computer and a hard disk drive for it to crash. This was in the days before portable computers were invented. Computers could not be moved and even the slightest knock could cause the read/write head in the drive to go crashing into the spinning disk and gouge out a furrow, with the consequent loss of data.

These days hard disk drives seem almost uncrashable and you can even use one on your lap or on a shaking and vibrating train. If you're new to computers you will just take this for granted, but if you have been around a bit a know what it used to be like, it's pretty amazing.

One of the techniques that modern laptop computers use to prevent disk problems is to employ a sudden motion sensor. This is exactly what the name suggests and it detects any sudden movement of the laptop. The hard disk drive can then be instructed to lift the read/write head of the disk and put them out of the way in a safe position.

It is possible to check the status if the sudden motion sensor by typing a command into the Terminal window. Run Terminal in the Applications\Utilities folder and then enter pmset -g. Pmset is actually a command that displays the power management settings, so what the sudden motion sensor is doing here is anyone's guess, but you will see a line with sms on it and the value is either 0 (off) or 1 (on).

To change any settings you have to enter administrator mode and enter your password. Type sudo pmset -a sms 0 to turn off the sudden motion sensor or replace the 0 with 1 to turn it on. Generally it is a bad idea to turn it off, but it's possible that if it is over-sensitive and minor movement is seen an earthquake, then disk operations could be constantly interrupted. It might make music or video playback stutter. Turn sms off at your own risk though.

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