Apple Portables: Advanced tips for Sudden Motion Sensor

Summary

Beginning with the PowerBook G4 (12-inch, 1.5GHz), PowerBook G4 (15-inch, 1.67/1.5GHz),  PowerBook G4 (17-inch, 1.67GHz), and iBook G4 (Mid 2005), Apple portable computers feature a Sudden Motion Sensor. Intel-based Apple portables such as the MacBook, MacBook Pro, and MacBook Air also make use of the Sudden Motion Sensor.

Sudden Motion Sensor technology is built-in protection for the hard disk, designed to help prevent disk issues if the computer is dropped or if it senses unusually strong vibration. Apple has adjusted this feature carefully to provide the best balance between protecting the hard drive and preventing unwanted activation of the Sudden Motion Sensor. Most Apple portable owners never need to turn this feature off. Apple suggests that you not modify the settings unless absolutely necessary.

In some environments, such as live concert halls, recording studios, or dance clubs, external vibrations may be major enough to cause the module to unexpectedly park the hard drive heads, resulting in interrupted sound or video playback. In these situations, you may find that you want to disable the feature temporarily.

Products Affected

Portable Computers

To disable the Sudden Motion Sensor:

Find the current status of Sudden Motion Sensor:

  1. From the Finder's Go menu, choose Utilities.
  2. In the Utilities folder, open Terminal.
  3. When the command line appears, type sudo pmset -g and press Return.
  4. Type in the administrator password when prompted and hit Return. This command queries the computer for the current setting of the Sudden Motion Sensor, which you can determine by locating the ams entry (in Mac OS X 10.3) or the sms entry (in Mac OS X 10.4 and 10.5) and looking to the right to determine its value. The default setting is "1" (turned on).

Disabling the Sudden Motion Sensor in Mac OS X 10.3:

  1. In Terminal, which should still be open from the previous instructions, you can disable the Sudden Motion Sensor by typing sudo pmset -a ams 0 and pressing Return (changing the setting to a zero disables the module).
  2. Type your administrator password when you are prompted and press Return.
  3. Type the sudo pmset -g command again to be sure that the setting has been applied.

Disabling the Sudden Motion Sensor in Mac OS X 10.4, 10.5, and 10.6:

  1. In Terminal, which should still be open from the previous step, you can disable the Sudden Motion Sensor by typing sudo pmset -a sms 0 and pressing Return (changing the setting to a zero disables the module).
  2. Type your administrator password when you are prompted and press Return.
  3. Type the sudo pmset -g command again to be sure that the setting has been applied.

Any changes that you make to the Sudden Motion Sensor setting remain in effect even after you restart the computer. If you choose to disable the Sudden Motion Sensor, Apple recommends that you re-enable it as soon as possible in order to take full advantage of the feature.

To re-enable the Sudden Motion Sensor:

Find the current status of Sudden Motion Sensor:

  1. From the Finder's Go menu, choose Utilities.
  2. In the Utilities folder, open Terminal.
  3. When the command line appears, type sudo pmset -g and press Return. Type your administrator password when you are prompted and press Return. If you have the Sudden Motion Sensor turned off, the value of the ams entry (in Mac OS X 10.3) or sms entry (in Mac OS X 10.4 and 10.5) will be a zero (0).

Re-enabling the Sudden Motion Sensor in Mac OS X 10.3:

  1. If the above command returns a zero, you can re-enable the Sudden Motion Sensor by typing sudo pmset -a ams 1 and pressing Return.
  2. Type your administrator password when you are prompted and press Return.
  3. Type the pmset -g command again to be sure that the setting has been applied.

Re-enabling the Sudden Motion Sensor in Mac OS X 10.4, 10.5, and 10.6:

  1. If the above command returns a zero, you can re-enable the Sudden Motion Sensor by typing sudo pmset -a sms 1 and pressing Return.
  2. Type your administrator password when you are prompted and press Return.
  3. Type the pmset -g command again to be sure that the setting has been applied.
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