Does Face ID work on iPhone X?

Face ID works best when your iPhone X is approximately an arm's length or closer (10-20 inches) from your face. ... Go to Settings > Face ID & Passcode. If asked, enter your passcode. Tap Set Up Face ID, then position your face in front of your device and tap Get Started.

A short list of times my iPhone X’s FaceID couldn’t recognize my face (qz.com)

• When I’d just woken up, in the dark of my room, without my glasses on
• When I put on my sunglasses and a baseball cap inside
• Walking outside with my sunglasses and cap on
• When my phone is on a table and my face is not directly parallel to it
• When I was brushing my teeth
• In a poorly lit bar
• When I sit at any desk with my hand covering my mouth, which is how I sit all the time