Steel Mace | Uncrate JD March 21, 2017 Gadgets 100 All the features you expect in a small, stylish package. That’s what the Fitbit Alta HR Fitness Tracker promises. The world’s slimmest wrist-based heart rate tracker, it required the development of a one-of-a-kind chip to pack in all its functionality. In addition to keeping tabs on your heart rate, calories burned, steps, and distance, it also uses data from the accelerometer and your heart rate variability to track how long you spend in the various stages of sleep, then gives you feedback and tips on how to maximize your time in bed. Available in a wide variety of colors and styles, paired with rubber, leather, or stainless steel wristbands and bracelets. Another fitness-focused tracker, this is not. The Qardio Core ECG Monitor delivers medical-grade data to both your phone and your caregiver the whole time you have it on. In addition to ECG readings, it also keeps track of your respiratory rate, heart rate, heart rate variability, skin temperature, and, yes, activity, giving your doctor a far more nuanced view of your daily health and routine than any wrist-bound gadget.