A group of German scientists have come up with a way to turn the human skin into a touch screen.

The new technology allows people to control their smart phones by stroking tattoos on their forearms.

Designed by scientists at the Max Plank Institute in Germany, the iSkin can be stuck to fingers, forearms or even behind people's ears.

The thin, flexible sensors can be glued on to the skin like a temporary tattoo.

They allow users to control smartphones by stroking these tattoos – turning the human skin into one gigantic touch screen.

Developer Martin Weigel says this could revolutionize the world of wearable gadgets.

"Current electronics are mostly using rigid components which are very uncomfortable to wear on the body and are limiting the locations to, for example, the wrist or on the head to be worn. But our sensor is a flexible and stretchable sensor, so it can cover many locations. For example, even the backside of the ear or the forearm. So, we have a much larger input space than current electronics allow for."

The iSkin system is made of bio-compatible silicone rubber, so the sensors can detect touch even when they are stretched or bent, unlike the current plasma or Led screens.

With the current prototype; wearers can answer incoming calls, play music and adjust the volume on their phone simply by tapping their skin. The inventors have even designed a roll-up keyboard that allows you to type on your forearm.

Weigel says the inspiration for the skin sensor comes from robotics.

"The technology is initially coming from robotics where it's used to give robots kind of a feeling similar to the human body, to human skin. However, we are the first to look into how we can use it on the body to control mobile devices; so as a kind of second-skin which nicely conforms to your body."

This technology can also be used to create more human-like prostheses that can sense contact, pressure and temperature.

But Wiegel and his team have even bigger plans.

"There is also research in using the body as an energy source and harvesting energy from the body, like for example from the temperature or from the blood flow directly.

The Scientists now want to find ways to power the iSkin sensors with energy created in our own bodies. Although it may sound like something out of a sci-fi novel, the day that the human body itself is turned into a perpetual battery in motion may not be too far off in the future.