Tapping your forearm or hand with a finger could soon be the the way you interact with gadgets.
US researchers have found a way to work out where the tp touches and use that to control phones and music players.
Coupled with a tiny projector the system can use the skin as a surface on which to display menu choices, a number pad or a screen.
Early work suggests the system, called Skinput, can be learned with about 20 minutes of training.
"The human body is the ultimate input device," Chris Harrison, Skinput's creator, told BBC News.
He came up with the skin-based input system to overcome the problems of interacting with the gadgets we increasingly tote around.
Gadgets cannot shrink much further, said Mr. Harrison, and their miniaturization was being held back by the way peopl are forced to interact with them.
The size of human fingers dictates, to a great degree, how small portable devices can get.