A cell phone that never needs recharging might sound too good to be true, but Nokia says it's developing technology that could draw enough power from ambient radio waves to keep a cell-phone handset topped up.

Ambient electromagnetic radiation--emitted from Wi-Fi transmitters, cell-phone antennas, TV masts, and other sources--could be converted into enough electrical current to keep a battery topped up, says Markku Rouvala, a researcher from the Nokia Research Centre, in Cambridge, U.K.

Rouvala says that his group is working towards a prototype that could harvest up to 50 milliwatts of power--enough to slowly recharge a phone that is switched off. He says current prototypes can harvest 3 to 5 milliwatts.