Baudisch is encouraged by the results and is in the process of establishing guidelines for building rear-touch interfaces into tiny devices. "Envision the future where you buy a video game that's the size of a quarter . . . and you wear electronic pendants," he says.

Jeff Han, founder of a startup called Perceptive Pixel, based in New York, says that Baudisch's concepts are impressive, but he's more interested in using touch technology on large displays. He has already had some success: he has supplied wall-size touch screens to a number of U.S. government agencies and several news outlets. In fact, his company's touch screens were used by news anchors during the November presidential election to show viewers electoral progress across the country.

Traditionally, large touch screens have been built in the same way as smaller ones, making them very expensive to create. Han's displays take advantage of a physical phenomenon called total internal reflection: light is shone into an acrylic panel, which acts as the display and is completely contained within the material. When a finger or another object comes in contact with the surface, light scatters out and is detected by cameras positioned just behind the display. Because a thin layer of material covers the acrylic, the scattered light also depends on the amount of pressure that is applied to the display.

In a paper presented in October at the User Interface Software and Technology Symposium, in Monterey, CA, Han's colleague Philip Davidson describes software that takes touch beyond the surface, using pressure to add another dimension to a screen.

Davidson created software that recognizes how hard a person is pressing a surface. If a user presses hard enough on an image of, say, a playing card and slides it along the display to another card, it will slide underneath. Additionally, if a person presses hard on one corner of an object on the screen, the opposite corner pops up, enabling the user to slide things underneath it. This provides a way to prevent displays from getting too cluttered, Davidson says.

However, Davidson also notes that pressure sensitivity should not make the device uncomfortable to use, and he has studied the natural fatigue that a person feels when she presses on a display and drags an object from one side to the other. The new pressure-sensitive features are expected to ship by the middle of next year, Davidson says.