In my country (BR), which is normally around 3 years behind the first world in most tech stuff, there is a popularity explosion w/ the app Runkeeper for running.
(Example: we now have Netflix but it has almost no relevant shows)
They're activity trackers. You start them to your wrist/pants and turn it on. Then it tracks the steps you've taken, calories burned, stairs climbed, your sleep pattern. Some even have hearth rate monitoring.
The point is that it's active 24/7 not just during workouts. These gadgets are part of the quantifiable self movement.