M7

9to5Mac (emphasis mine):

For pre-iPhone 5s devices, ARGUS usually drains about 20-30% of battery life per day while running in the background. The app continually checks for motion and calculates the distance and number of steps using the accelerometer and GPS. With the M7, however, the app does not need to be running in order to keep track of the number of steps – all of that data is tracked by the M7. As such, ARGUS no longer takes up any battery power while running in the background and the stated battery life from Apple – 10 hours 3G talk time, 250 hours of standby – will stay exactly the same. […]

The M7 APIs allow developers to query information about the user’s current transportation status (whether they’re in a car, walking, not moving, etc.).

If this is true, it's impressive.

I hope that the use of the M7 will expand outside of the fitness and health apps.