When you’re wearing your Apple Watch (Series 3 and later), you can use it to securely unlock your iPhone (models with Face ID) when you’re wearing a face mask (iOS 14.5 or later and watchOS 7.4 or later required).
To allow Apple Watch to unlock your iPhone, do the following:
Go to Settings > Face ID & Passcode.
Scroll down, then turn on Apple Watch (below Unlock with Apple Watch).
If you have more than one watch, turn on the setting for each one.
To unlock your iPhone while you’re wearing your Apple Watch and a face mask, raise iPhone or tap its screen to wake it, then glance at your iPhone.
Note: To unlock your iPhone, your Apple Watch must have a passcode, be unlocked and on your wrist, and be close to your iPhone.