The main parts of a door knocker are the knocker (the metal piece that you strike on the door) and the strike plate (the metal plate attached to the door that the knocker hits). Some door knockers also have a decorative backplate that holds the knocker and strike plate in place on the door.

An old door knocker might be referred to as a "doorknocker" or as a "knocker." It is a piece of hardware attached to a door that is used for knocking to alert those inside.

The inventor of the door-knocker, Osbourn Dorsey, did not win any notable awards for his invention. He patented the door-knocker in 1878 as a way to notify homeowners of visitors in a polite manner.

A door knocker can be made in any shape desired - even to look like a face, like in A Christmas Carol.