The Struggle for Accurate Measurements on Your Wrist

Wearable devices are getting more advanced, but can today’s technology really measure our health?
Until recently, I didn’t know a thing about how my roughly 25-minute bike commute across San Francisco—or any other part of my day, really—affects my body, other than that I inevitably arrive at work sweaty and a bit out of breath when I’m in a big rush. How high is my heart rate? Do my sleep habits affect it? How many calories do I burn?