#doorknocker  a device (usually metal and ornamental) attached by a hinge to a door
  supertype:  device  an instrumentality invented for a particular purpose; "the device is small enough to wear on your wrist"; "a device intended to conserve water"
  part of:  front_door__frontdoor__frontentrance  exterior door (at the entrance) at the front of a building

No statement uses or specializes doorknocker; click here to add one.