This device harvests power from your sweaty fingertips while you sleep

Researchers have developed a new device that harvests energy from the sweat on -- of all places -- your fingertips. To date, the device is believed to be the most efficient on-body energy harvester ever invented, producing 300 millijoules (mJ) of energy per square centimeter without any mechanical energy input during a 10-hour sleep and an additional 30 mJ of energy with a single press of a finger.