The iPhone 5S M7 coprocessor can be used all the time in background without draining the battery.

[quote]

The new M7 coprocessor is like a sidekick to the A7 chip. It’s designed specifically to measure motion data from the accelerometer, gyroscope, and compass — a task that would normally fall to the A7 chip. But M7 is much more efficient at it. Now fitness apps that track physical activity can access that data from the M7 coprocessor without constantly engaging the A7 chip. So they require less battery power.

M7 knows when you’re walking, running, or even driving. For example, Maps switches from driving to walking turn-by-turn navigation if, say, you park and continue on foot. And if your phone hasn’t moved for a while, like when you’re asleep, M7 reduces network pinging to spare your battery. [/quote]