i think using rings for unlocking phones would be a good idea. you put on a ring, bring your phone close to it and enter the unlock password. next time you touch your phone with that ring, it unlocks automatically. if you take it off, it detects that, erases the unlock password from its memory and stops working that way.
more reliable than a fingerprint reader, easily disabled (just take it off), can't be emulated like other biometrics, but doesn't require entering the password each time either
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