A British tech company has come up with a new way of powering wearables and smart home devices: a device called the Freevolt, which can harvest the ambient energy from radio waves and turn it into a small amount of electricity for low-energy gadgets to tap into.

As CNET reports, this level of energy can't keep a smartphone running, but it could be enough to power that remote sensor on your garden gate. If sensors and beacons have a wireless energy source plus wireless connectivity, it opens up more possibilities for kitting out our homes and gardens with these kind of devices.

"Companies have been researching how to harvest energy from Wi-Fi, cellular, and broadcast networks for many years," Drayton Technologies CEO and chairman, Lord Drayson, said in a press statement. "But it is difficult, because there is only a small amount of energy to harvest and achieving the right level of rectifying efficiency has been the issue - up until now. For the first time, we have solved the problem of harvesting usable energy from a small radio frequency signal."

The Freevolt device itself is around the size of a mobile phone, but only the thickness of a credit card, so it can easily be attached to a sensor or smart tag. Drayson Technologies has developed a CleanSpace air pollution sensor (costing around £55 or US$85) as a reference device for the ways Freevolt can be utilised.

The British company says that three specific technologies have helped make the energy harvested by the Freevolt usable: a multi-band antenna to attract energy from a wide spectrum of radio bands; a rectifier component that turns that energy into a current in a highly efficient way; and an optimised power management system that clings on to every last drop of power that's available.

Eventually, Freevolt devices could be built into buildings and structures if the technology catches on, but it's early days yet. It's able to collect energy from Wi-Fi and television signals, plus 2G, 3G, and 4G networks, so it has the potential to be used in any built-up urban area. Further down the line, Drayson wants to build smaller versions of the Freevolt - and that could lead to wearables and smartwatches that never need charging.

"Whether we live in a big city or an increasingly urbanised area in the developing world, radio frequency waves are being generated all around us, at different levels, all the time," adds Drayson. "Some of this wireless energy goes unused... [but] we've figured out a way to make it useful."