Face ID on the iPhone X is great for quickly unlocking your device, but there are times when you don't want it to work -- like if a friend grabs your phone, a mugger steals it, or you have to deal with the police.
If your hands are free and the iPhone X is still in your possession, it's easy to turn off Face ID. Just press down on all three physical buttons (volume up, volume down, and the side button) to switch off this feature. But what if someone already snatched your phone or your hands aren't free because you're driving?
Don't worry, Apple thought of that too.
As reported by Reddit, all your have to do is say "Hey Siri, whose phone is this?" and Face ID will switch off automatically -- this also works for Touch ID on older iPhones. Once you're in the clear, just say "Hey Siri, goodbye" to switch it back on.
You probably won't use this feature very often, but it could be extremely handy in a pinch. The law is still a little murky when it comes to Face ID/Touch ID and the police -- freedom of speech protects you from having to enter your passcode, but cops can still force you to unlock your device with a face or fingerprint scan.
This could also work if someone tries to steal your iPhone X and unlock it with your face, but in that case you may just want to play along. You're probably better off just giving away your smartphone than risking bodily harm to keep it locked. You can always wipe it remotely afterwards.