Knŏck'er, n.

noun

(nŏk'er), n. One who, or that which, knocks; specifically, an instrument, or kind of hammer, fastened to a door, to be used in seeking for admittance.

*Shut, shut the door, good John! fatigued, I said; Tie up the knocker; say I'm sick, I'm dead. Pope.*

An ornate door knocker with a sculpted face and a circular ring hanging from its mouth. — Knocker.