Touch sensors are mostly likely to be small, flat, hard surfaces, such as the surface of a smartphone screen. These touchscreens require delicate webs of electronics to detect contact and movement on the surface. Some use computer vision to operate, which requires a camera to view the surface and is easily disrupted.

Researchers at Carnegie Mellon University’s human-computer interaction institute, however, have developed a basic method to add touch sensitivity to objects of all shapes, sizes and textures.

This was achieved by applying electrically conductive coatings or materials to surfaces of common objects. A coating can be applied by applying carbon-loaded films, bulk plastics, or simply by covering the surface with conductive paints using a spray can.

When a finger touches the touchpad, it “shunts” current to the ground. Applying multiple electrodes to the surface and using a technique called electric field tomography allowed the researchers to localise where and when shunting occurs.

Electric field tomography is a contactless imaging method for investigating living tissues; it works by running small currents through pairs of electrodes and detecting changes in voltage.

"For the first time, we've been able to take a can of spray paint and put a touch screen on almost anything," said Dr Chris Harrison, assistant professor in the human-computer interaction institute at Carnegie Mellon University.

The new technology, named “Electrick”, has been demonstrated to work on walls, furniture, instruments, steering wheels, toys and even jelly and Play-Doh. The Carnegie Mellon team have used Electrick to create an interactive smartphone case which opens apps such as a camera based on how the user grasps the phone.

While the technology allows touch sensitive surfaces to be created on virtually any solid object at low expense, Electrick suffers from low accuracy compared with other touch sensors. It is capable of detecting the location of a finger to an accuracy of one centimetre, making it suitable for simple button or slider controls.

Yang Zhang, a PhD student at Carnegie Mellon who worked on Electrick, suggests that the technology could be accessible to hobbyists, and is compatible with common manufacturing techniques, such as vacuum forming, 3D printing and casting.