Engineers have been converting mechanical stress into electricity using piezoelectric devices for more than a hundred years, but the goal of powering an iPod by pounding the pavement has remained elusive. Current piezoelectric materials are difficult to manufacture and typically contain toxic metals, such as nickel and lead. Researchers at Lawrence Berkeley National Laboratory have solved both problems by using a genetically engineered virus that self-assembles into a film. When pressure is applied, helical proteins on the viruses' shells twist and turn, generating a charge. Tapping a postage-stamp-size swatch produces 400 millivolts of electricity, or enough to briefly power an LCD screen. Within 5 to 10 years, says bioengineer Seung-Wuk Lee, the film could be used to harness power from building vibrations, heartbeats, and other types of movement, too.