A retiring cam is an electrically or mechanically actuated arm on the car door that extends to release the landing door lock only when the car is at a landing, and retracts while the car is travelling. Because the cam is withdrawn during travel it cannot brush against the locks of intermediate floors, which prevents accidental unlocking and reduces wear. Retiring cams are common on freight lifts and older installations; most modern passenger lifts use a vane and roller coupler instead.