Canan Dagdeviren and others are designing machines that use the human body itself as their source of energy. Increasingly, researchers are testing such wearable or implantable devices in animal models and people. To take advantage of piezoelectricity, Dagdeviren and her colleagues have developed flat devices that can be stuck onto organs and muscles such as the heart, lungs, and diaphragm. These devices are “mechanically invisible” in that their mechanical properties are similar to whatever they are laminated onto, so they don’t hinder those tissues when they move. Scientists are also developing wearable piezoelectric energy harvesters that can be worn on joints such as the knee or elbow, or in shoes, trousers or underwear. That way, a person can generate electricity for electronics whenever they walk or bend their arms.