The gadgets of the future could be powered by the human body itself, according to scientists in the US and China.
They have developed a small metallic tab, called a triboelectric nanogenerator which, when attached to the body, can generate electricity from simple movements - including bending a finger.
The tab is only 1.5cm long and 1cm wide, and can deliver a maximum voltage of 124 volts, a current of 10 microamps and a power density of 0.22 millwatts per square centimetre.
This is certainly not enough to rapidly charge a smartphone, but these are the early days of the invention's development, and it was able to power 48 LED lights simultaneously.
The collaborative research project was led by teams at the University at Buffalo in the US and the Institute of Semiconductors (IoP) at the Chinese Academy of Science (CAS).
"No one likes being tethered to a power outlet or lugging around a portable charger," said lead author Qiaoqiang Gan in a study published by the Nano Energy journal.
"The human body is an abundant source of energy. We thought: 'Why not harness it to produce our own power?'" said Dr Gan, from the University of Buffalo's School of Engineering and Applied Sciences.
The teams believe they have done just that using triboelectric charging, which occurs when certain materials become electrically charged after coming into contact with a different material - the same way most static electricity is created.
The scientists investigated a number of potential nanogenerators which were capable of producing the triboelectric effect, but most were too difficult or expensive to manufacture.
Now, they have made a breakthrough using two thin layers of gold, with polydimethylsiloxane (also called PDMS, a silicon-based polymer used in contact lenses, Silly Putty and other products) sandwiched in between.
Because one of the layers of gold is stretched, it crumples when released, causing friction between the gold layers and the PDMS.
"This causes electrons to flow back and forth between the gold layers. The more friction, the greater the amount of power is produced," said another lead author, Professor Yun Xu of CAS.
The tab is easily manufactured and the team is investigating using larger pieces of gold which could deliver even more electricity.
They also want to design a portable battery to store energy which the tab is producing, and think the system could power a number of wearable and self-powered electronic devices.