A door closer is a mechanical device that automatically closes a door after it has been opened. It is commonly used in commercial and residential buildings to ensure that doors close securely, enhancing safety and energy efficiency. The device typically consists of a spring and hydraulic mechanism that controls the speed and force of the door's closure. Door closers are often found on entry doors, fire doors, and interior doors. They help prevent doors from slamming, which can cause damage or injury. Many door closers are adjustable, allowing users to set the closing speed and force according to their needs.