(InfraRed remote control) A handheld, wireless device used to operate audio, video and other electronic equipment within a room using light signals in the infrared (IR) range. Infrared light ...

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. If they match, the phone unlocks.

This places it between visible light and microwaves, and above long-wave IR at 20 THz – 37 THz. LWIR is what thermal cameras use, with LWIR also emitted by warm objects, such as the human body.