Deadman control or Deadman Switches can either be buttons (also known as Constant pressure control) or a car switch (spring loaded crank).
How it works
For deadmans control with buttons, the buttons has to be held at all time, if the button is not being pressed the elevator will stop, the call buttons work the same way. For the crank elevators the crank has to be turned to a direction to go up or down , if the crank gets let go the crank will return to the default position and the elevator will stop, when the call buttons are pressed it does not really call the elevator,what is does is make a light (or something else) on a panel inside the elevator letting the elevator operator to go to the floor where the elevator has been called.