Systems converting energy of the body into electricity, such as this foot prosthesis, are being used to power portable electronic devices, such as smartphones or pacemakers. (KIT/Andreas Keller/KUNZBERG GmbH)

Smartphones, fitness trackers, and medical equipment have a constant hunger for power. The solution: power supply by means of energy produced by body movements. Two systems that meet this requirement were developed. One design uses body weight during walking, and the other generator can be worn on the wrist like a wristwatch.