Door chain

A door chain, security chain, or security door chain consists of a small chain attached to the door frame, which attaches to a track on the door for security purposes. It is a type of lock that is often used along with other types of locks to secure a door.

Uses

Door chains are mainly intended to allow a person inside a structure to open the door slightly for purposes of communicating with individuals outside or exchanging small objects through the door while still preventing the individuals outside from gaining unauthorized access into the structure.

Door chains also can be set in place when the door does not need to be opened. They can only be touched from outside when the door has been opened, and therefore, if the locks on the door are compromised, a door chain may cause some delay, draw more attention, or leave more evidence of force being used when gaining unauthorized access to the structure.

Door chains installed on hollow-core doors, or that are not anchored into solid materials (such as the wood door frame) do not provide protection. This is because the chain can easily be defeated by pushing on a door. The chains are helpful go sound an alert to the person inside that someone is breaking through a door. The noise may be heard by the occupants giving them time to call for help, escape via another exit, or get a weapon to protect themselves. Door chains are also sometimes used to slow down mentally-challenged individuals who may attempt to exit from inside a structure.