Garage door openers operate through a large motor unit that raises and lowers overhead doors after the command from a control unit. There are three types of drive mechanisms: bicycle-type chain and sprocket, plastic strip, and worm-screw drive. No design has been judged superior and all work well.
The control unit must be key or wireless operated. If key operated, the driver must leave the car to unlock the door. If wireless operated, the driver has a mechanism inside the car with a button, set on a frequency to open the door. Better units offer security codes, overhead lights, and economical models with a 1/4-hp motor, all models must incorporate an optical sensor that detects resistance when closing.