A door closer is defined as any mechanical device that closes a door in a controlled manner, preventing it from slamming, in general after someone opens it, or after it was automatically opened. The force used to open the door is stored in some type of spring and when released this energy is then used to return the door to a closed position.

Door closers can be linked to a building's fire alarm system.

Where doors need to be held open for most of the time they are held back with an electromagnetic device.
When the fire alarm is triggered it cuts power to the electromagnetic hold-open device allowing the doors to close.
These hold-open devices can be separate from the door closer or part of its design.