The presence of the sensor is well documented as part of Apples Sudden Motion Sensor hard drive protection system.

How to access it is undocumented.

Aaackshually, the Sudden Motion Sensor was introduced on 2005 in the PowerBook G4, and continued through the intel MacBooks with hard drives.

While officially undocumented, people figured out how to access it back then, with novel uses like smacking your MacBook to change spaces (virtual desktops) or swinging the Mac around to make lightsaber noises.

- https://www.youtube.com/watch?v=6uvQTTPr9Rw

- https://osxdaily.com/2006/12/06/macsaber-turn-your-mac-into-...

(I should know, I was in university back then and swung my Mac around like an idiot, lol.)

On the first Retina MacBook Pro 15" in 2012, and moving forward with all MacBooks that were SSD-only, they removed the SMS as it was not needed.

To my knowledge, this is the first time we're hearing that Apple Silicon machines have an accelerometer on the SoC, officially or otherwise. It's also certainly not branded or marketed as the SMS was. (https://support.apple.com/en-us/100871)

Happy to be corrected on this!

In 2022 "a little birdy pointed out an accelerometer" to iFixit on their teardown of an M2 MBA: https://www.ifixit.com/News/62674/m2-macbook-air-teardown-ap...

They could not figure out what it was for.

Ars Technica commenters at the time believed it was to record drops so Apple repair teams could rebuff requests :)

I think there's some sort of motion sickness reducing feature in MacOS Tahoe which would require an accelerometer.

Given that current drives don't have moving parts, what function is this serving today?

Apple has a motion sickness mitigation feature that displays dots on your screen that move based on physical motion, so it’s fairly well known that the accelerometer exists.

That's for iOS devices though

https://support.apple.com/en-om/guide/mac-help/mchla3c4f1da/...:

“Vehicle Motion Cues

Vehicle Motion Cues may help reduce vehicle motion sickness while using a Mac and riding as a passenger in a car or other on-road vehicle.

To customize Vehicle Motion cues, click Customize Appearance, then set any of the following options:

- Pattern: Select Regular for a stable and predictable pattern of onscreen dots, or Dynamic for a more engaging visual experience.

- Color: Select a color of onscreen dots. Color saturation will automatically adjust to maintain contrast with the content behind each dot.

- Larger dots: Turn on Large dots to increase the size of the dots that appear onscreen.

- More dots: Turn on More dots to increase the number of dots that appear onscreen.

Note: This option is available on Mac laptop computers. It’s not available on MacBook Air (M1) or 13-inch MacBook Pro (M1) or earlier.”

It’s also for macOS

> the sensor lives under AppleSPUHIDDevice in the iokit registry, on vendor usage page 0xFF00, usage 3. the driver is AppleSPUHIDDriver which is part of the sensor processing unit.