https://techcrunch.com/2017/09/12/iphone-x-basically-has-a-kinect-on-the-front-to-enable-faceid/

It remains to be seen whether Apple’s FaceID will be as convenient as TouchID (it already failed on stage), but at the very least we can’t accuse Apple of not dedicating enough hardware to the task. The front of the new iPhone X has a full-on depth-sensing system much like that of the original Kinect.

The prominent cutout on top hides more than a selfie camera — it has a pair of infrared blasters that locate your face even in the dark and project a network of dots onto it. An IR-sensitive camera watches how those dots are distorted and reflected on your face, producing a detailed 3D mesh.