Mark Hanrahan, writing for Reuters: Researchers in the United States have unveiled a prototype of a battery-free mobile phone, using technology they hope will eventually come to be integrated into mass-market products. The phone is the work of a group of researchers at the University of Washington in Seattle and works by harvesting tiny amounts of power from radio signals, known as radio frequency or 'RF' waves. "Ambient RF waves are all around us so, as an example, your FM station broadcasts radio waves, your AM stations do that, your TV stations, your cellphone towers. They all are transmitting RF waves," team member Vamsi Talla told Reuters. The phone is a first prototype and its operation is basic - at first glance it looks little more than a circuit board with a few parts attached and the caller must wear headphones and press a button to switch between talking and listening.