The door interlock, also called the door lock or landing door lock, is a mechanical and electrical safety device fitted to each landing door that ensures the elevator car cannot move unless all landing doors are fully closed and locked. The electrical contact of the interlock is wired in series into the safety circuit, so that any open landing door immediately interrupts the circuit and stops or prevents car movement. Interlock mechanisms must withstand a specified force to prevent unauthorised opening from the landing side.