This is an interesting question because if you were to be mugged, the robber could hold your face up to the phone and have it unlock even if you were unwilling, or the cops could do the same as well. However in a recent interview with TechCrunch, Apple’s Craig Federighi revealed that users could quickly disable Face ID in such situations.
According to Federighi, “On older phones the sequence was to click 5 times [on the power button], but on newer phones like iPhone 8 and iPhone X, if you grip the side buttons on either side and hold them a little while — we’ll take you to the power down [screen]. But that also has the effect of disabling Face ID. So, if you were in a case where the thief was asking to hand over your phone — you can just reach into your pocket, squeeze it, and it will disable Face ID. It will do the same thing on iPhone 8 to disable Touch ID.”
Now exactly how fast this will work remains to be seen, but it seems that the uncertainty of the feature has led to some unscrupulous sellers online who are selling full face masks that they claim will protect users from identity theft from Face ID.