The most important part of the system of automatic door arm jacks is the photocell eye, which detects the presence of any obstacle, whether person or car, in the space between the door. These photocell eye models are a pair that are installed outside the door and next to the door. The eyes act as a transmitter and the other as a receiver. Any interruption of the sending signal from the transmitter indicates an obstacle in the space between the door, which commands the command circuit to cancel the door closing process and the door begins to open. .