Christian Moeller (site)
"A five meter tall stainless steel pole is standing in the center of a huge warning sign on the gallery floor telling the visitor “do not touch”.
It creates a conflict by tempting the visitor to do precisely what he is warned not to do. This conflict, when resolved through disobedience results in a jolting physical experience. Whenever somebody decides to ignore the warning by touching the pole he receives a significant electric shock amplified by sound."