Apple portable computers come with a sudden motion sensor that is used to detect when the computer is moved or dropped. This lets the computer prepare the hard drive for movement, which can prevent the heads from either being damaged or from scraping against and damaging the disk surface--which can happen if the computer is struck, dropped, or subjected to severe vibrations.
When the sensor is activated, the computer's hard drive may make a noise as the heads park, which can be a subtle click but can also be a substantial clack that can even be felt. This will depend on the drive make and model, but it can be alarming to some people.
While this safety feature should not impede on general function, there are times when it can cause pauses in computing tasks. For instance, if you are loading something off the hard drive and move the computer around, you can cause the computer to pause the load if you move it around. This will pause video playback for some applications. As such, there may be times when you need to disable the sudden motion sensor to prevent interruptions.
You can disable the sudden motion sensor by changing a variable in the power management settings of the system. Entering the following command in the terminal will turn off the sudden motion sensor:
This setting will remain in effect until you repeat it with a "1" at the end instead of a "0" to turn it back on.
Will this hurt the computer?
Since you are disabling a safety feature, your computer will be more vulnerable to damage during movement; however, the computer should be able to handle gentle movement and small vibrations, tapping, and other mild physical impacts without harming the system. The sudden motion sensors are a precautionary measure that are used to guess when the computer will be subject to more violent movement, but this detection is not always correct. If you are gentle with your computer when the sudden motion sensor is disabled, you will have nothing to worry about; however, we recommend keeping the sensor on whenever possible.Resources