Even if it was transmitting instead of using a side-channel like current draw... With only 3.5 microwatts, the phone would still have to be very close to the ba

Even if it was transmitting instead of using a side-channel like current draw... With only 3.5 microwatts, the phone would still have to be very close to the base station. As a comparison, "normal" cellphones transmit something around 100 to 1000 milliwatts, so at least 10^5 more powerful. EDIT: This Wired article has a lot better information: https://www.wired.com/story/this-cell-phone-can-make-calls-even-without-a-battery https://www.wired.com/story/this-cell-phone-can-make-calls-e... "... Some key components of Talla's phone are housed remotely to save power. A nearby basestation has circuitry for converting and connecting to the digital cellular network, currently via Skype. The prototype basestation uses an unlicensed frequency, limited to low-power transmissions. Because the phone relies on those signals for its energy harvesting, it has a range of just 15 meters from the basestation." And it looks like they use backscatter, which would be "transmitting" signal and not using a side-channel.