A door closer is a mechanical device that closes a door, in general after someone opens it, or after it was automatically opened. Choosing a door closer can involve the consideration of a variety of criteria. In addition to the closer's performance in fire situations, other criteria may include resistance to opening forces (for use by disabled or infirm), control over the rate of closing, safety, durability, risk of vandalism, and aesthetics.
Surface-mounted door closers come in four variations: slide-track arm, regular arm surface mounted, parallel arm surface mounted, and top jamb mounted. Overhead door closers are typically surface mounted, though most manufacturers offer concealed models too. Such closers mount inside a pocket in the door frame or are mounted in the floor directly under the pivot point and are completely concealed.
Another type of door closer, a surface mounted one, is attached to the door frame behind the door (where the hinges are) next to the middle hinge. The "arm" rests against the door, and a spring that is bent by the user opening the door closes the door by retracting to its proper shape.
There is also the storm door and screen door variation of the door closer: As the name implies, these piston shaped closers are used on storm, security, and screen doors which give the home an extra line of defense against weather, intruders, and insects. Whereas interior closers typically use hydraulics, storm door closers are more typically pneumatic, using air and springs to close the door. Storm Door closers generally have a small metal washer on the rod that is used to lock the closer in the open position when moving stuff in or out, but more recent models such as the Touch 'n Hold door closer have a button to actuate the hold open feature to make this process easier.
Finally, there is the concealed, jamb-mounted door closer, which fits in morticed recesses in the door and door frame and is totally concealed when the door is closed. These are available in controlled and uncontrolled versions, selected according to the application for which they are intended.