From day-one I was happy with the iPhone’s Touch ID. So I was skeptical when Apple eliminated the home button (and Touch ID) and replaced it with Face ID. But works as advertised. It works so well I forget it’s working. And I guess I don’t care that much how it works. From iMore.com:

Face ID uses multiple neural networks that are built into the dual-core A11 bionic neural engine to process the facial recognition data. It takes a mathematical model of your face and checks it against the original scan of your face that you first registered.

The information is stored on the A11 chip on your iPhone X and not sent to Apple’s servers, so your facial identity is kept private.

It uses a Require Attention feature in order to work. That means you have to be looking at your iPhone for it to scan, You can’t be asleep or looking away for it to unlock your iPhone. […] It doesn’t work with photographs. It doesn’t work while you’re asleep. It doesn’t even work with detailed silicon masks that look just like you.

I tried to think of a way to make some sort of screencast to show how well this feature works but… there’s almost nothing to show. When my phone ‘sees’ my face — and only my face — it unlocks.