Automatic garages use an electrical motor to open and close the door. Because garage doors are so heavy, this motors connects to a cable and pulley system and a large torsion spring to convert the fast motor rotation into a slow and smooth pulling action.
Automatic garage motors are not especially powerful; 1/2-horsepower engines are common, and systems typically pull around six amps. These low requirements mean that garage motors can run on standard 120-volt systems and don't require the more powerful lines heavy household appliances demand. Garage systems also use electrical power to detect when someone presses a properly programmed garage door opener and safety systems that stop the door from moving if they detect motion.