A door chain or security chain is a small [[chain]] affixed to the door frame that attaches to a track on the door.  This is to prevent the door from being opened completely as a security measure, while allowing the door to be opened enough to communicate or exchange small items with a person outside.  These are a common feature on hotel and motel room doors.

h4. External Link

* "Wikipedia - Door Chain":[https://en.wikipedia.org/wiki/Door_chain]
door chain