Scientists have developed a wearable device that uses your body heat as a battery. Our bodies maintain a constant temperature of around 37 degrees celsius to allow the chemical reactions that keep us alive to happen. But it isn’t a particularly efficient process and a lot of that heat we generate is lost through our roughly two square metres of skin. This new device uses thermoelectric generators to harness the difference in temperature between your skin and the surrounding air, turning that heat energy into electricity. Created by a team at the University of Colorado Boulder (CU Boulder) in the US, it is made from a stretchy material that fits close to the skin and can be worn as a ring or a bracelet.