Berlin : German researchers have built shoe-sized devices that harvest power from the act of walking. The technology could be used to power wearable electronic sensors without the need for batteries. There are two separate devices: a “shock harvester” that generates power when the heel strikes the ground and a “swing harvester” that produces power when the foot is swinging. They could also form the basis of a self-lacing shoe for the elderly. Details of the advance are outlined in the journal Smart Materials and Structures. “We have tried to power a wireless transmitter and to power a simple sensor,” said a researcher.