Reading the undocumented MEMS accelerometer on Apple Silicon MacBooks via iokit
github.com

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129 points

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todsacerdoti

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17 hours ago

57 comments

seductivebarry ・ 14 hours ago

Way back in ~2008 I wrote the Newton Virus https://www.everita.com/how-the-newton-virus-was-made + https://www.youtube.com/watch?v=eh75j6OHhRc (sorry for the broken images, need to update that site). Between that and using a hidden API to take screenshots of each individual element on your desktop (from icons, to taskbar, to windows) the effect was pretty believable. One of the most fun (and frustrating) projects I ever worked on.

  • outadoc ・ 9 hours ago

    I've tried to find this for so long. I remember seeing it at the time as a teenager and thinking it was SO COOL. Basically made me discover Apple and want a Mac. :)

  • directmusic ・ 8 hours ago

    When I saw the post the Newton Virus was the first thing I thought of. Thanks for making it. I remember showing my family the video and remarking about how cool it was.

  • swiftcoder ・ 13 hours ago

    Offtopic, but I have nostalgic feelings for the era of MacBook in the video

  • tmslnz ・ 14 hours ago

    Troika! Hello from a friend in London :)

krackers ・ 15 hours ago

>have a hard to find mems accelerometer managed by the sensor processing unit

How did OP even know that an accelerometer exists in the first place?

  • rustyhancock ・ 14 hours ago

    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.

    • future10se ・ 14 hours ago

      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!

      • 1e1a ・ 12 hours ago

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

    • nerdsniper ・ 14 hours ago

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

      • juggerl6 ・ 11 hours ago
        ・ 3 more

        Void warranty if dropped

        • nerdsniper ・ 9 hours ago
          ・ 2 more

          Has anyone reported this happening?

          • xattt ・ 4 hours ago

            People who knew what they did aren’t going to go online and say that they tried to return a dropped device.

  • argsnd ・ 13 hours ago

    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.

    • mschuster91 ・ 11 hours ago

      That's for iOS devices though

      • Someone ・ 7 hours ago

        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.”

      • nom ・ 10 hours ago

        No.

  • saagarjha ・ 14 hours ago

    > 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.

userbinator ・ 15 hours ago

undocumented

The one thought that comes to mind is this: "Your warranty claim was denied because we determined that the laptop was subjected to a sudden shock."

  • consp ・ 15 hours ago

    Back in the days this was to lock up the hard disk read/write head. Maybe a relic from those times instead?

    • userbinator ・ 14 hours ago

      Apple is not known for backwards-compatibility, and they were already using SSDs in their laptops long before switching to ARM.

  • sysguest ・ 15 hours ago

    idk you can just use simple liquid-container or sticker?

    maybe apple was preparing for "carrying-around laptop experience"?

    • XorNot ・ 15 hours ago

      That's an entirely different product build path compared to the electronics production line though.

      If a pick and place machine can drop it on and reflow it, that's what you want.

      • sysguest ・ 14 hours ago

        well it would be hardened when contact with air or something

        see "Shipping Damage Indicators"

  • altairprime ・ 15 hours ago

    Did it park the drive heads?

1e1a ・ 11 hours ago

On my M4 14-inch MacBook Pro, it looks like there are two accelerometers: One with {"DeviceUsagePage"=0xff00,"DeviceUsage"=3}, and one with {"DeviceUsagePage"=0xff00,"DeviceUsage"=9} - They both identify as Bosch BMI286

  • 1e1a ・ 10 hours ago

    Ah, after some testing, it looks like these both refer to the same IMU, DeviceUsage=3 is for the accelerometer and DeviceUsage=9 is for the gyroscope. The serial number is also the same for both.

JSR_FDED ・ 14 hours ago

If it can read your heartbeat from your wrists resting next to the trackpad, maybe it can use that as a user satisfaction signal for gratuitous UI changes.

  • pbhjpbhj ・ 13 hours ago

    If it's sensitive enough to read a heart beat, then surely it can be used as a covert microphone?

    • gavinsyancey ・ 10 hours ago

      The laptop also contains a normal microphone. You can't access this without root; if you have that you have permissions to access the real microphone.

      • nottorp ・ 10 hours ago

        ... but think how much "engagement" a "security expert" would get out of this!

    • Quppi ・ 11 hours ago

      From testing, it seems to require me to press my wrists quite hard against the macbook to get a somewhat accurate reading on the heartbeat. Non the less a cool project and I wasn't even aware my macbook has an accelerometer.

    • rcxdude ・ 13 hours ago

      Depends on the bandwidth.

    • rcxdude ・ 13 hours ago

      depends on the bandwidth

47282847 ・ 9 hours ago

I would like an app to lock my screen on sudden movement; optionally disable TouchID for next login.

  • ohyoutravel ・ 9 hours ago

    Maybe you’re also interested in having it start the fuse on your thermite pot, that you have time to stop if it turns out it’s not the FBI raiding your house for what’s on your hard drive?

    • 47282847 ・ 9 hours ago

      Are you implying that it is paranoid and irrational regardless of circumstance to want this?

      Sorry to disappoint. I’m working in the human rights space, with dozens of real world experiences by people I work with. I got raided once myself. They were unable to locate any computer on my premises. They however took my phone and a couple of encrypted hard drives for forensic analysis. They asked for the device PIN, which I did not provide. A court later ruled the raid and seizure and temporary confinement illegal. I did not reuse the returned phone. They didn’t pay for the replacement, or the lawyer.

      • ohyoutravel ・ 5 hours ago

        Yes that was my implication, but I see based on your comment you have real concerns! My apologies for the implication.

1e1a ・ 12 hours ago

I've been wondering about this for a while, glad someone's finally managed to access it.

ggm ・ 14 hours ago

Could this be used as "shake your mac for highly random seed" bits?

  • 1e1a ・ 7 hours ago

    There's lots of noise in the accelerometer readings, even without shaking

  • mlajtos ・ 10 hours ago

    Shake your Mac to undo would be consistent with iPhone, iPad, Vision Pro. Yes, you shake your head to undo when wearing AVP.

    • RupertSalt ・ 10 hours ago

      This is a milder version of “Shake to Reboot” which is standard for all Etch-a-Sketch models

  • c22 ・ 13 hours ago

    Probably not as random as you want it to be.

    • sysguest ・ 13 hours ago

      well wouldn't it add up?

      someWhatRandom1 xor someWhatRandom2 xor notRandom3 xor ...

      should be more 'random' than just 'someWhatRandom1'

      • throawayonthe ・ 12 hours ago

        i'm not sure it would necessarily be more random if you're mixing in a lower-entropy source which the accelerometer probably is

      • LoganDark ・ 12 hours ago

        XOR is the worst hashing function imaginable, especially if the data isn't truly random, because it can cancel out to become even less random!

        It's better to use a KDF or something. Even a block cipher should work far better than XOR.

LoganDark ・ 12 hours ago

I wonder if this sensor is used for Vision Pro display mirroring.

  • 1e1a ・ 12 hours ago

    I think it's used for the motion sickness reducing feature in MacOS Tahoe that puts a bunch of dots on your screen that react to motion.