The SMDL-AIS (Salvo Manual Door Lock) Is a mechanical interlock used to positively bolt loading bay doors in the closed position. The switch contacts can be used for controlling power to the dock leveller or other ancillary electrical devises e.g. traffic lights. The unit incorporates a locking bolt which passes through the door running rail and into the lock body. Only when the key is inserted and turned, can the locking bolt be disengaged, allowing the door to be opened. The turning of the key closes the switch contacts.