device any clever maneuver; "he would stoop to any device to win a point"; "it was a great sales gimmick"; "a cheap promotions gimmick for greedy businessmen"
knocker -
a person who knocks (as seeking to gain admittance); "open the door and see who the knocker is"
knocker -
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.