How to quickly disable Face ID on Apple iPhone
If you need to quickly disable Face ID on an Apple iPhone, squeeze both the side button on right and either one of the two volume buttons on left at the same time, for about two seconds.
The system should bring up a screen with a slider to confirm powering the device off, as well as an Emergency SOS call slider.
Simply ignore these to continue with the device powered on, but with Face ID disabled.
You will have to enter your personal PIN code or password to operate the iOS device again.
This may be useful in situations where a user would not want any other person to be able to hold their Face ID device up to the user’s face to unlock it, such as around a sneaky teen, a jealous partner, or if potentially subject to harassment by law enforcement officers, such as during a protest march.
Topic: How to quickly disable Face ID on Apple iOS devices including iPhone