Sudden Motion Sensor (SMS;How To Manage on Your Mac

Enable or disable SMS via terminal

Since 2005, portable Macs have included a sudden motion sensor (SMS) to protect their hard drives. The SIM uses motion detection hardware in the form of a triaxial accelerometer that can detect motion in three axes or directions.

Mac uses SMS to detect sudden movement, which could mean that the Mac is dropped, damaged, or usually at risk of serious impact. Once this type of motion is detected, SMS protects the Mac’s hard drive by moving the drive heads from their current active location on the rotating magnetic discs to a safe location that retracts away from the drive. This is usually called head parking.

With the drive head parked, the hard drive can withstand a fairly large impact without damaging the boards or losing data.

When SMS detects that your Mac is back in stable condition, ie. no longer hitting, it reactivates the drive. You can return to work with all your data intact and not damage your device.

The disadvantage of the sudden motion sensor is that it can experience false events. For example, if you use a Mac in a noisy place, such as a concert, nightclub, airport, construction site, or almost anywhere with repetitive low-frequency noise that has enough power to move your Mac, even if your movement is invisible, SMS may Detect these movements and turn off your drive by parking your heads.

The only thing you may notice is a slight stutter in the performance of your Mac, such as a movie or song that stopped so slightly during playback. If you’re using a Mac to record audio or video, you may notice a pause in the recording.

But the effects are not limited to multimedia applications. If SMS is activated, this can lead to the suspension of other applications, the rotation of beach balls and more than a little deterioration on your part.

That’s why it’s a good idea to know how to manage SMS on a Mac; how to turn it on, turn it off or just check if it works or not.

Check the status of SMS on your Mac

Apple does not provide an application specifically designed to monitor the sudden movement of sensors, but OS X includes the increasingly convenient Terminal application , which we previously used for the interior of our Mac.

  1. Start the terminal located in / Applications / Utilities /.
  2. When prompted for the command line, enter the following (you can copy / paste the text instead of entering it if you prefer):
    1. sudo pmset -g
  3. Press the key to enter or return the keyboard.
  4. You will be asked for your administrator password; enter the password and press enter or return.
  5. The terminal will display the current settings of the power management system (“pm” in memory), which includes the SMS settings. A lot of elements will be listed. Find the SMS item and compare the value with the list below to understand its meaning:
  • sms – 0: The sudden motion sensor is deactivated.
  • sms – 1: The sensor is on.
  • No sms entries: Your Mac is not equipped with an SMS system.

Activate the SMS system on your Mac

If you’re using a Mac that comes with a hard drive, it’s a good idea to turn on the SMS system. A few exceptions are noted above, but overall, if your Mac has a hard drive, you’re better off with the system enabled.

  1. Start the terminal.
  2. At the command prompt, type the following (you can copy / paste):
    1. sudo pmset -a sms 1
  3. Press enter or return.
  4. If you are asked for your administrator password, enter the password and press enter or return.
  5. The SMS system activation command does not give any feedback on whether it is successful or not; you will just see the explanation of the terminal prompt. If you want to make sure the command is accepted, you can use the “Check SMS status on your Mac” method described above.

Disable the SMS system on your Mac

We’ve already mentioned a few reasons why you might want to disable the sudden motion system on the Mac’s motion sensor. We will add another one to this list of reasons. If your Mac is only equipped with an SSD , there is no advantage in trying to park the device heads, as there are no SSDs; in fact, there are no moving parts.

The SMS system is mostly a hindrance for Macs that only have an SSD installed. This is because in addition to trying to park non-existent SSD heads, your Mac will also stop any SSD writing or reading while the SMS system detects movement. Since the SSD has no moving parts, there is no reason to turn it off due to low movement or a little stuttering while the SMS waits for your Mac to return to stable condition.

  1. Start the terminal.
  2. At the command prompt, type the following (you can copy / paste):
    1. sudo pmset -a sms 0
  3. Press enter or return.
  4. If you are asked for your administrator password, enter the password and press enter or return.
  5. If you want to make sure SMS is turned off, use the procedure described above in “Checking the SMS Status of Your Mac.”

By the way, the SMS system is also used by several applications that use the accelerometer. Most of these apps are games that use SMS to add a “tilt” feature to games. But you can also find some interesting scientific applications for the accelerometer, such as the Seismac application, which turns your Mac into a seismograph, and only if you live in an earthquake or near a volcano.


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