Smartphones use big touchscreens on the front as a useful tactile interface. However, our hands naturally wrap around the back of the phone, too. This area is underutilized as an interface, but the designers of BackTrack found a way to change that.
The idea is simple. The project video notes that conductive tape can be placed on a multitouch touchscreen, allowing touches to be read at a remote location. Taking this concept further, BackTrack works by creating a 2D matrix on the back of the phone, and connecting this matrix to a series of pads in a row on the front touchscreen. Then, touches on the back touchpad can be read by the existing touchscreen on the front screen.
Doing this in practice requires the use of fancy transparent electrodes and flexible connections. However, the team behind Backtrack were able to create their passive rear touchpad in a formfactor that fits into a simple phone case. It can then be used to play games or use interface with the phone in other ways.
We fully expect phone manufacturers to start creating interfaces that use the back surface of the phone. Apple have already explored this with the rarely-discussed back-tapping feature. Implementing a full 2D touchpad on the rear could quickly become a great point of difference for the first handset manufacturer to get it right. Video after the break.
[Thanks to Itay for the tip!]