After roughly 30 minutes of obnoxious buzzing, I was conscious about preemptively correcting my posture. Never underestimate the power of an oddly located dzzzz dzzzz dzzzz.
You can keep Coach mode engaged for as long or as little as you'd like, but even when it isn't actively buzzing you, the device is constantly tracking your posture, and will rate how well or poorly you've been doing every time you open the app.
As for activity tracking, it is perpetually counting your steps, measuring distance traveled and calories burned. It even provides a nice visual breakdown of how active you were hour by hour. If you easily give in to accusations of laziness, this should hit you right where it hurts. And safe to say, most of us could stand to get up and move a little more often and, well, stand a little taller. It's on us all not to devolve into a bunch of nasty hunchbacks.