They're practically everywhere, and it's no wonder: according to some analysts, the fitness tracker market is one poised to reach 19 billion in 2018. But some companies are positioned better than others. On Wednesday, one of the arguable forerunners, Moov, took the wraps off the Moov HR, an activity tracker that measures heart rate with pinpoint accuracy. The Moov HR builds on the foundation of the startup's previous sensor, the Moov Now, which garnered praise for its innovative approach to fitness. Rather than simply measuring the number of steps you've taken, the calories you've burned, and distance you've walked, it fed that data into an artificial intelligence that dynamically guided you through goal-oriented workouts.