How is the Body Sensor Permission utilised by the apps?
I'm aware that it uses hall sensor and proximity sensors to detect human presence. I want to know how exacty it detects specific people? I'm talking of the smart lock: On-Body Detection. It used to be fairly inaccurate but hall and proximity sensor cannot distingusih between bodies (i think, correct me if I'm wrong)
So is there something I'm missing?

Can it read my ("vital signs") respiration rate or heartrate or body temperature (as it says on the screenshot)? I'm particularly interested because Google has it and Google has made it just for itself?? I've not seen any app request for this permission

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Googling shows body sensor is used to detect physical activites but it's not. The dedicated physical activity sensor is used for that.

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Based on the information provided by Google's support page on the topic, it sounds like they're using almost exclusively accelerometer data. The things they mention for Pixel devices (and are most likely identical or at least similar to other phones running Android) are:

  • Your phone will learn the patterns of your walking and may lock if "another walk pattern" is detected
  • Your phone will lock when set down on a surface (completely stationary)
  • Your phone may not lock when using transportation that's inherently shaky, such as planes or boats

That being said, Body Sensors are separate from this process and mostly have to do with fitness tracking and wearables. For instance, my smart watch and companion app needs the Body Sensors permissions to track heart rate and oxygen saturation, as well as to collect step and sleep data. I haven't found a comprehensive list, but if you install the Health Connect Beta app, you can use it to view, enable, or disable which apps have access to which Body Sensor data. In your case, if no app has asked permission for this, then nothing on your phone has access to it.

  • Hmm.. that's interesting. I couldn't find anything relevant on how it does that.. did you stumbled upon something like that?
    – 44yu5h
    Apr 26, 2023 at 14:18
  • How on-body detection works? I remembered the description when enabling it on my phone ("stays unlocked while it is in motion") and used that to find the Google support page with more information. I think they keep the exact details obscured on purpose though, as publishing these might enable others to figure out better how to fool such a detection algotrithm. Apr 26, 2023 at 14:49
  • I remember it used to be like the device will stay unlocked as long as it is with you or it will get unlocked on detecting "your body". Yes they must keep the exact process hidden but still I'll search and see what I can get and get back to you. Also they removed smart locks from most android versions (or was it my OS? Not sure) meaning it must be buggy. As far as I remember it got to unlocked for my brother's body too the last time i tested it. (I was standing far)
    – 44yu5h
    Apr 26, 2023 at 14:58
  • With this system, the device will never unlock by detecting you in any way. It simply allows it to stay unlocked while it determines you're in possession of the device, and will lock it otherwise. Fwiw, it is still present on my Pixel 6 Pro running Android 13 under Settings > Security & privacy > More security settings > Smart Lock > On-body detection. Apr 26, 2023 at 17:21
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    There are some physical limitations with what you're worried about. For instance, your phone can't read your heart rate without a wearable with such a sensor, or you holding your finger to the camera, and I don't think there's a phone yet that can sense body temperature. In the end though, as long as (1) you trust that Google and your phone's manufacturer are being transparent in their collection and usage and (2) you pay attention to apps and services that request such information, as you clearly are, then you shouldn't have to worry about this information being taken without your consent. Apr 27, 2023 at 13:54

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