The dots are invisible to your eyes. But you can see them through an infrared camera. The iPhone X's camera analyzes the dots on your face and compares it to the image made when Face ID was set up.

Since this article was published, The Information came out with a report citing multiple sources who said that at least one ...

Apple's rumored foldable iPhone currently in development ... core components that make up the TrueDepth camera system – like the dot projector and infrared camera – need a clear, unobstructed ...