Disable the Sudden Motion Sensor on a Mac

Dec 16, 2010 - 2 Comments

disable sudden motion sensor

The Sudden Motion Sensor is designed to protect your Macs hard drive in the event of a computer being dropped or an unusually strong vibration. Essentially what it does is park the hard drive head when movement is detected, which prevents it from potentially scooting across the disk surface and scratching or otherwise damaging the drive or drive head.

Generally speaking, you will want to always have the SMS sensor enabled, but Apple mentions that certain environments are susceptible to unnecessary drive head parking due to the SMS. Basically the SMS detects a strong vibration and then the hard drive parks which can cause video and music playback issues, amongst other annoyances. This is particularly true with concert halls with strong acoustics, recording studios, dance and night clubs, and even walking workstations (the ones with a treadmill under a standing desk). Also, some owners of SSD drives may want to disable the feature.

Disable Sudden Motion Sensor on a Mac Laptop

This works to disable the Sudden Motion Sensor on the MacBook Pro, MacBook Air, MacBook, PowerBook, and iBook running Mac OS X 10.6 and lower:

  • Launch Terminal
  • Type the following at the command line: sudo pmset -a sms 0
  • Hit return and enter your password

The SMS sensor is now disabled, it’s just as easy to reenable again by changing the zero to a one when you need the protection back:

Enable the Sudden Motion Sensor on a Mac Laptop

This works on the same hardware as disabling the feature, and it’s basically the same commands:

  • Launch Terminal
  • Type the following at the command line: sudo pmset -a sms 1
  • Hit return and enter your admin password

You’ll notice the commands are identical except that the -a sms flag now has 1 attached to it rather than 0 (standard computing protocol of 1 for on, 0 for off).

Checking the status of the Sudden Motion Sensor

If you’re not sure whether the motion sensor is enabled or not, you can check quickly with the command line:

  • Launch Terminal
  • At the command line, type: sudo pmset -g
  • Hit return, enter your password, and look for “sms” in the list. Seeing a 1 next to sms indicates that the motion sensor is enabled, seeing a 0 next to sms indicates the motion sensor is disabled

Most users will never need to adjust the sudden motion sensor, but if you do find yourself in a situation where there are continuous vibrations or movements and your Mac is behaving strangely, this may be the culprit.

Find out more Mac OS X and iOS troubleshooting tips if you’re interested.

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Posted by: David Mendez in Mac OS X, Troubleshooting

2 Comments

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  1. Marc says:

    This is especially useful when using a Macbook Pro 2008 with a 3rd party Hard drive. Some (such as the WD Scorpio black) have their own specialized SMS so to speak, and this can cause kernal panics with the Macbook’s built in SMS.

  2. Ken says:

    Agree with Marc. I have a Macbook Pro 2008 with a Seagate Momentus XT Hybrid Drive. The drive is much quicker than the stock drive, but it does kernel panic anytime the laptop experiences too much movement. Turning off the SMS stopped the kernel panics.

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