from scientificamerican.com: From our footsteps to our button presses, humans are constantly expending energy, and researchers are tapping into these movements to power the world around us. Harvesting energy from one’s surroundings or activities rather than from a battery or a wall outlet has some key advantages: The electricity sources are free and the devices are more mobile. This is particularly useful for medical electronics like insulin pumps and pacemakers. Energy harvesters could also prolong battery life in smartphones and laptops. The idea isn’t new. Crystal radios, for example, have been around since the start of the 20th century and do not need a dedicated power source, since they scavenge electricity from radio waves. But current energy harvesting strategies are not very efficient, and the energy in our environment is diffused widely, meaning bright lights, large temperature gradients or long, brisk walks are needed to produce an appreciable amount of power, which may still not be very much.