FaceID asks for the passcode to enable itself every few days it seems. Not sure the frequency.
And clicking the side button ten times locks it to needing the pass phrase.
And clicking the side button ten times locks it to needing the pass phrase.
Holding the power/side button and either volume button for a couple of seconds (just pressing them together and letting go creates a screenshot) presents a menu allowing you to power the phone off, display your medical ID, or call emergency services. You can also configure settings to have this action do the countdown as described above instead. Either way, biometric unlock is disabled until you re-enter your passcode/PIN.
Either option is pretty easy to do unnoticed with your phone in your pocket.