The new Activity and Workout apps for the new Apple Watch uses a variety of onboard sensors to measure your movement and heart rate, and even your GPS location with some help from your iPhone. "The Activity app monitors movement throughout the day," says Apple. "The Workout app tracks dedicated workouts."

The Activity app shows three rings to represent your daily overall activity: one ring for "Move," one for "Exercise," and one for "Stand." Move tracks your overall activity, Exercise measures brisk activity, and Stand measures how often you stand up from sitting.

The Workout app, on the other hand, shows real-time stats for calories burned, time, distance, and pace for your runs, jogs, and walks. Using the app you can chart your progress over time (with help from the Fitness app for iPhone), and also track specific kinds of workouts like bike rides. There are also features like stopwatches, timers, and notifications to recommend that you stand up after sitting for a while. Lastly, Apple Watch may use your history to suggest personal goals for your workouts, like a personal trainer might.

The two apps in combination with iWatch may effectively replace the fitness apps you're already using, like Jawbone UP, Human, and Moves. It's worth noting, however, that the iWatch starts at $349 — which is much more expensive than most fitness bands and free fitness apps.