Meet "Vi," the Siri of fitness
What makes Vi different from a Fitbit, Pebble, Apple Watch, and every other wearable you've seen is that it's actually like having a personal trainer, only instead of a real person shouting in your ear, you get instructions and feedback from an interactive AI that goes by the name of Vi -- basically, a more enthusiastic, human-like, hardass version of Siri. The device itself resembles a pair of wireless earbuds, tethered to a U-shaped neckband. Those earbuds are capable of a lot more than just pumping out workout jams (although, side note, they were developed with audio pros Harman/Kardon). They have aerospace-grade biosensors that constantly monitor your heart rate, speed, and level of exertion while simultaneously tracking environmental factors like elevation, location, and weather.
A quick note on the heart-rate sensors: LifeBEAM, the company behind Vi, invented the sensors used in fighter pilots' helmets that keep critically close tabs on their vital signs. So, suffice it to say, they know what they're doing. And because the sensors are located between your heart and your brain, rather than on your wrist (as they are with most wearables out there), they're capable of capturing your heart rate with much better accuracy.