Abstract: A safety system comprises a light beam transmitter and receiver and means connected through a standard AC power plug to the main power supply of an automatic garage door opener for controlling the power thereto. The transmitter transmits a beam of light across the opening of a garage door. The receiver is positioned to receive the light beam if there is nothing obstructing the beam. The receiver generates a signal indicating when the beam is being received. The means disconnects the power to the garage door opener when a signal is generated indicating that the light beam is not being received. The garage door is thus prevented from making contact with and hurting or damaging a person or object in its path.