Sudden Motion Sensor: Advanced Tips

Beginning with the PowerBook G4 (12-inch 1.5GHz), PowerBook G4 (15-inch 1.67/1.5GHz), and PowerBook G4 (17-inch 1.67GHz), PowerBook G4 computers feature a Sudden Motion Sensor.

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 PowerBook G4 owners will never need to turn this feature off, and 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.

To disable the Sudden Motion Sensor:

First, 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 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 step, 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:

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 remains 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:

First, 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) 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:

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.