Arrow Electro Magnetic door closers or Exidor Electro hydraulic door closers are designed for use on fire/smoke doors. The unit is controlled by the building fire/smoke detector and alarm system. On operation of the alarm, the hold open facility is released allowing the door to close in the normal manner. A swing free door closer version allows the door to swing freely as if no door closer is fitted. If the alarm is activated, or if power is cut, the door closer will reactivate and close the door.