Hal Hodson, technology reporter

The touchscreens on tablets and smartphones make the devices easy for one person to interact with, but what happens when there is more than one user?

Touchscreens can’t tell your fingers from anyone else’s, but that’s set to change, as a team of researchers led by Chris Harrison at Carnegie Mellon University in Pittsburgh, Pennsylvania have built a system which distinguishes user inputs using the body’s electrical profile. The technique, which the team call “capacitive fingerprinting” was presented by Harrison at the UIST conference in Cambridge, Massachusetts this week.

The system works by sending multiple frequencies of a weak electrical current through a user’s finger when they first touch a device. Different frequencies take different paths to the ground through the human body, and the team’s prototype measures the path each frequency takes, building up an electrical profile that is unique to the user (see video). Each user’s interaction with the touchscreen is then assigned to their profile. The system builds on Disney’s Touche system, which lets everyday objects detect touch gestures.

Harrison envisions tablets that allow multiple people to use a touchscreen simultaneously, primarily to play games or for activities like painting. Two-player tablet games do exist, but they use a split screen to allow separate input. The team – which includes researchers from Disney Research Institute in Pittsburgh and the University of Tokyo – built a two-player tablet version of whack-a-mole that allows either player to whack moles anywhere on the screen, while the computer keeps track of each user’s score.

Although the system can distinguish between touchscreen users, Harrison says that the body’s electrical signature is not precise enough to be used as a biometric to provide secure access to a device. Wearing a different pair of shoes changes the body’s electrical signal, for example, since the flow of current to the ground is changed. This causes anyone’s electrical signal to fluctuate too much to be useful for personal identification

http://www.newscientist.com/blogs/onepercent/2012/10/a-touchscreen-that-knows-how-y.html