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It also shows that it can leak all kinds of other information.

…which is why both Android & iOS put high-frequency access to the accelerometer behind an additional permission AFAIR.

It really is crazy. Placing my phone on my chest lying down i can clearly see my heartbeat on the graph

good idea https://tautme.github.io/phone-sensors/heartRate.html , try setting it on the ground and see how sensitive it is to foot steps.... or earthquake https://seismosense.com

it detunes guitars?

It tunes every string to D