A dwarf, goblin, or sprite imagined to dwell in mines and to indicate the presence of ore by knocking particularly in Cardigan etc. in South Wales (18th..19th century)
A knocker is a piece of metal on the front door of a building, which you use to hit the door in order to attract the attention of the people inside. see also knock
a device (usually metal and ornamental) attached by a hinge to a door a person who knocks (as seeking to gain admittance); "open the door and see who the knocker is"