Smartwatches and fitness trackers have come a long way since the first Fitbit practically invented the modern wearables market in 2009. Back then, the only thing you could measure was how many steps you took. About five years later, smartwatches burst onto the scene, and today the best smartwatches can give their users a heart rate, blood oxygen saturation, and skin temperature sensor on their wrist for just a couple hundred bucks.
