Miniature phones or other devices may soon be a reality for consumers after Microsoft researchers created devices with touchscreens on the reverse side.

Most mobile devices have small displays and require some form of human touch input, whether from keys or a touchscreen. Until now this has limited how small a device can become, because there needs to be room to input information via a keypad and view the results on a screen. Even with touchscreens there are problems with making the screen too small: when a user inputs commands on a touchscreen, they obscure part of the screen with their finger. This makes accuracy difficult to achieve.

At Microsoft's TechFest annual showcase of new technology in development, researchers showed off a prototype device with a touchscreen on the rear side, a display screen on the front and input buttons on the side.

The Nanotouch is a mere 2.4 inches square, about half the size of a smartphone, and it heralds the dawn of a new drive to develop smaller portable devices.

Researcher Patrick Baudisch said: "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.

With Nanotouch, you can see your finger, as it were, through the screen, and see what you are inputting. This allows us to make the devices much smaller without losing any accuracy."

Using the touchpad on the back, users can select or drag items on the screen, making the entire screen visible at all times.

According to research, because users can see the effect of their touch, they can hit targets barely 2 millimetres wide. This potentially brings the advantages of touchscreens to much smaller devices such as electronic jewellery, computers that clip on to clothing and even watches where the strap becomes the touch pad.

Mr Baudisch demonstrated how he can easily control a video game using the Nanotouch. He said mini-devices using the technology might be used by people playing sport or at other times when they did not want to have bulky phones with them.

The device was one of 40 innovations from Microsoft's research and developments labs around the world on display at TechFest at the company's campus in Redmond, Washington. Nanotouch was developed by Microsoft researchers and the Hasso-Plattner-Institute in Germany.

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