Android
Turn On-body Detection On or Off auf Android
On-body detection is part of Android's Smart Lock family and relies on a motion sensor instead of a fingerprint or PIN. Once you unlock the phone once, the sensor keeps tracking its own movement pattern and assumes you are still holding it, so the lock screen does not reappear until the device stays still for a while.
That is convenient if you switch between apps constantly, but it also means the phone can stay unlocked inside a pocket, backpack, or car seat. Anyone who picks it up during that window gets full access without ever seeing a PIN or fingerprint prompt.
Where to switch it off
The setting sits inside the extended unlock options, not on the main security screen. Go to Settings ➔ Security & privacy ➔ More security & privacy ➔ Extend Unlock ➔ On-body detection and toggle Use On-body detection off.
Turning it off means the lock screen returns immediately after the display turns off, even mid-walk. If you only want faster unlocking at home, Trusted Places is usually the safer alternative, since it ties the relaxed lock screen to a fixed location instead of a movement guess. On-body detection also has no effect on fingerprint or face unlock themselves, it only skips the step of showing the lock screen.