A door knocker is an item of door furniture that allows people outside a house to alert those inside to their presence. A door knocker consists of a plate attached to the door and a hinged weight (usually metal) that may be lifted and released to strike the plate, making a noise.
Door knockers are often very ornate, but some are a simple brass ring.
Door knockers in literature
Now, considered as an abstract circumstance, there was no more obvious cause or reason why Mr Kenwigs should take the trouble of muffling this particular knocker, than there would have been for his muffling the knocker of any nobleman or gentleman resident ten miles off; because, for the greater convenience of the numerous lodgers, the street-door always stood wide open, and the knocker was never used at all. The first floor, the second floor, and the third floor, had each a bell of its own. As to the attics, no one ever called on them; if anybody wanted the parlours, they were close at hand, and all he had to do was to walk straight into them; while the kitchen had a separate entrance down the area steps. As a question of mere necessity and usefulness, therefore, this muffling of the knocker was thoroughly incomprehensible.