Smartphones and mobile devices have revolutionised our lives, but their battery lives are still limited, requiring constant re-chariging. Scientists as the University of Washington in the US, however, have developed a working battery-free cellphone that harvests power from ambient radio signals and light, and is capable of making voice calls using off-the-shelf components available from most electronics stores. By removing the on-the-spot conversion of analogue signals picked up by your phone's microphone into digital data that's relayed across the mobile network, which requires around 800 milliwatts to when making call —  a huge amount of power compared with the 3.5 microwatts the battery-free cellphone needs to operate; instead of the conversion, the phone retains everything analogue, registering tiny vibrations from its microphone during a call to transmit the signals to a nearby base station, operating several metres away. To find out more go to First battery-free cellphone makes calls by harvesting ambient power.