We’re all familiar with the Internet, and the way it connects humans to one another and to vast amounts of data. But computer visionaries foresee the day when not just humans but all our devices are connected to each other via the Internet.

This so-called “Internet of Things” (IoT) would make possible all manner of transformative technologies, from digital sensors that allow crops to report when they are thirsty or under attack by insects to parking spaces that alert us when they’re available to tiny implants that continuously monitor our health as we go about our lives.

That long-anticipated day is still a ways off, because at this point the Internet of Things might more accurately be described as an Internet of Costly Things.

“Today’s radio technologies cost at least $4, making them too expensive for embedding into objects at scale,” says Dr. Joshua Smith, a professor of computer science at the University of Washington in Seattle and a leading expert on wireless systems.

The high cost comes not just from the radio transmitters needed for systems like Wi-Fi and Bluetooth but also from the batteries they need for power. So Smith and his team set out to build a low-cost communications system that doesn’t need batteries or the energy they provide.

Sounds Impossible, but…

Communicating without energy might sound impossible. But it isn’t — consider a shipwrecked sailor who signals rescuers by reflecting sunlight from a mirror. Smith and his colleagues have developed a so-called “backscatter” system that works in a similar way: a tiny antenna either absorbs or reflects radio waves from a transmitter, such as a normal household wi-fi router. This creates a faint but distinctive echo of the original signal that can be detected and decoded by a receiver even over significant distances.

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Because they have no power-hungry transmitter, Smith says, backscatter devices can get all the energy they need from thin air — or, rather, from the radio and TV broadcasts that fill it.

At home, that could mean a single wi-fi router talking to dozens of tiny devices mounted on fridges, doorbells, and the like. How about a smart coffee mug that tells you when your favorite beverage is getting cold? And out in the world, the IoT could save crops or bust traffic jams.