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 access to the structure.
Door chains also can be set in place when the door does not need to be opened. They cannot be touched from outside until 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 are also sometimes used to slow down mentally impaired individuals who may attempt to escape from inside a structure.
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