ktulus cry brings news of a device that can power portable gadgets, prosthetic joints, and other mobile appliances by harvesting energy generated by walking. Researchers are working on making the device — still a moderately cumbersome 3.5 pounds — smaller while maintaining its energy harvesting capacity. CNet has a write-up with more pictures and a diagram of the device. "In the mode in which the brace is only activated while the knee is braking, the subjects required less than one watt of extra metabolic power for each watt of electricity they generated. A typical hand-crank generator, for comparison, takes an average of 6.4 watts of metabolic power to generate one watt of electricity because of inefficiencies of muscles and generators. A lighter version would be helpful to hikers or soldiers who don't have easy access to electricity. And the scientists say similar mechanisms could be built into prosthetic knees other implantable devices such as pacemakers or neurotransmitters that today require a battery, and periodic surgery to replace that battery."