News link US researchers have found a way to work out where the tap 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. To identify where you've tapped, it relies on the different paths of the acoustic signals that you generate when you tap your own arm. It's not accurate enough yet to treat yourself as a full keyboard but it can distinguish up to 10 locations with fairly good accuracy. So you could be a numeric keypad. Just watch out for people tapping on your arm to ask what time it is. They might dial your phone!