IR is infrared light or light that is outside the visible light spectrum, in other words the naked eye cannot see it. IR light does not obey all the same properties as visible light. IR can pass through certain types/colors of plastics and some other materials, it's very easily reflected off most objects, and it's very prevalent in today's electronics.
This is an IR Object tutorial, which use to detect the objects motion, so it can be using in a lot of applications, it can be use in hotels reception doors to open the door when a motion detect.
the circuit implemented using PIC microcontroller as a main part in the circuit, the microcontroller for every so while send a series of pulses, which receive by IR receiver, when an object detect, the yellow LED turn on.