knocker

A hinged fixture, such as a metal ring or bar, used for knocking on a door.

A goblin or dwarf said to live under the earth and direct miners to ore by knocking.

One who knocks.

A knob, bar, or ring of metal attached to an outer door, by knocking with which persons seeking admittance can attract the notice of the inmates. It is usually so held by a hinge that it can be lifted and allowed to fall against a metal plate or stud, giving a sharp blow. It has now generally given place to the door-bell.