[abadaba]

I wonder if Face ID is still able to partially detect a masked user's face, just with a much lower confidence interval. Maybe the presence of the watch allows Face ID to lower the confidence threshold when it detects a mask blocking half of the face. This is just a guess, I have no idea how Face ID works.

If Face ID can't detect anything when a user wears a mask then I completely agree with you. It seems really silly to require the mask in order for the watch unlock to work. I don't understand the security model there.

[lemax]

It works because you put your watch on, unlock your watch. Your watch remains unlocked until you take it off. I was under the impression if you’re wearing your watch and it’s unlocked, and then you pick up your iPhone, it acts as the key to your phone.

[valine]

The watch will only unlock your phone when you're wearing a mask. If FaceID doesn't see a mask it will ignore the Apple Watch.