Knocker/ˈnɑːkər/ Definition 1 of 5Pro Tip 1/3Door Accessory A knocker is found on exterior doors of houses, usually decorative. The antique shop sells vintage knockers. Pro Tip 2/3Distinctive Sound Using a knocker produces a loud, distinctive sound to alert occupants. The sound of the knocker alerted everyone inside. Pro Tip 3/3Cultural Symbol Some knockers have symbolic designs, like lions or hands. Their door had a lion-shaped knocker for good luck.