Online Encyclopedia of Western Signs and Ideograms Symbols.com

Symbol 52:12

5212

52:12 · A modern sign used in technical and architectural contexts for a part of an "electric eye", i.e. a device used to automatically open and close doors that sends a light beam across the opening to a light sensitive lens on the other side. When someone crosses the beam a signal from the receiver starts the motor opening the door.
    The sign 4233 represents the receiving part of the "electric eye".