https://consumerist.com/2017/09/29/apple-admits-that-face-id-may-be-fooled-by-evil-twins-little-kids/

When Apple introduced the iPhone X’s new “Face ID” feature — which scans a user’s face to unlock the phone — the company said it had considered the “Evil Twin” scenario. And now, it’s admitting that if you have a twin — or an alternate reality doppelgänger– he or she could totally break into your phone.

In its Face ID Security Guide [PDF], Apple notes that the probability of a random person successfully unlocking your phone is about 1 in 1,000,000 — compared to versus 1 in 50,000 for Touch ID.