BBC News has some details on a wireless device that gets charged wirelessly, too:
The battery-free camera was modified so it could scavenge power from ambient wi-fi signals, store it and then use it to take photos.
The experiment was one of several by US researchers looking at ways to use wi-fi as a power source.
The system, known as power-over-wi-fi, has been developed by PhD student Vamsi Talla and colleagues at the Sensor Systems Lab at the University of Washington in Seattle.
The team realised that the energy contained in ambient wi-fi signals that are now ubiquitous often came close to the operating voltages required by a variety of low power devices.
The team used the power beaming system to run a temperature sensor and a small surveillance camera that both sat several metres away from a wi-fi hotspot.
The low-power camera gathered energy from wi-fi and stored it in a capacitor that prompted the camera to take a picture when it was charged. By leaching off the ambient radio signals, the camera gathered enough energy every 35 minutes to take a snap.