nano touch microsoft research & hasso plattner institute

Back-of-device touch input can enable pointing input on very small screens. This enables building new types of devices, such as touch-capable electronic jewelry. Here are four of the back-of-device designs we envision (a) pendant, (b) clip-on (b) watch, and (b) ring. Screen diagonals range from 2.5" to less than half an inch.

We explore how to add pointing input capabilities to very small screen devices. On first sight, touch-screens seem to allow for particular compactness, because they integrate input and screen into the same physical space. The opposite is true, however, because the user’s fingers occlude contents and prevent precision. So while touch was shown to work well for 3"+ screens, the size of these devices makes them hard to carry while physically active or with fashionable clothing. A half- or quarter size touch screen device, in contrast, is limited to a small number of on-screen objects and/or requires a stylus (e.g. palm watch).

We argue that the key to touch-enabling very small devices is to use touch on the device backside. In order to study this, we have created the 2.4” prototype device shown below; we simulate screens smaller than that by masking the screen. In a user study, participants completed a pointing task successfully across all (2.4" to 0.3") display sizes when using a back-of device interface. The touchscreen-based control condition (enhanced with the shift technique), in contrast, failed for screen diagonals below 1 inch. A second study provides design guidelines for practitioners who want to design for back-of-device interaction (details: CHI 2009 paper).