The window regulator is the mechanical assembly inside the door panel responsible for moving the glass up and down. It can be a scissor-type mechanism (using metal arms) or, more commonly in modern cars, a cable-and-pulley system. It works in conjunction with either a manual hand crank or an electric motor. This component bears the weight of the glass; common failures include snapped cables or stripped gears, which result in the window falling into the door or making a grinding noise without moving.