[ru552]

Just close your eyes. The Face ID on an apple device won't unlock if you have your eyes closed.

[cosmorocket]

But what if the bad guys "just" ask you not to close your eyes persuasively enough?

[ru552]

Try it. Use your hand to hold your eye lids up and see what happens.

edit* if you're talking about other means of persuasion, it's the same risk factor as if you had a PIN to unlock it.