be modified to see through clothing at a frequency just below visible light. Such imaging is not true x-ray vision, but rather shows variations in heat radiation rising from the skin beneath the clothing which can provide some detail of the body beneath. In comic books in the latter half of the 20th century, there often appeared an advertisement for "X-ray specs" which displayed the face of a smiling boy wearing glasses with spirals on the lenses looking at his hand through which he could see the bones. While X-rays cannot be used in practice to enable seeing objects through walls, researchers have recently shown how everyday wireless signals, such as wi-fi, can be used to achieve x-ray vision. See also Wall hack References Fictional superhuman features or abilities Fiction about X-ray vision