The MATRIX PowerWatch ($140) is most effective as an activity tracker because its ultra-low power consuming microprocessor is powered by the heat radiating from your skin. This makes the calorie burning readout extra precise since calories are just a unit of heat.

While powering a watch by your body’s heat is not a new thing, Matrix Industries founder Akram Boukai states that the processor made by Ambiq Micro is essential to accomplish all this as it can power more functions than just a sweeping second hand. Besides its very accurate calorie burning counter, the PowerWatch can also track your footsteps, quality of sleep, or set timers and stopwatches. Ah, it will also tell you the time!

The smartwatch is Bluetooth-enabled to transfer biometric data with your phone, is waterproof down to 50 meters, and, once you remove it from your writs, it goes to sleep but the 200mAh battery can store and remember your data for up to two years.