Nearly every smartwatch tracks how many calories you burn. The Matrix Powerwatch goes a step further, using them to power itself. Using thermoelectric technology, it accurately measures how many calories you burn everyday, then uses that body heat to keep itself running. As you'd expect, it also syncs wirelessly to your phone, tracks your steps and sleep, and is water resistant to 50 meters, meaning you can wear it in the pool, lake, or ocean without worry. Finished with a circular aluminum case and black nylon strap.