M7 CoprocessorThe iPhone 5s has a dedicated M7 coprocessor that measures accelerometer, gyroscope and compass data, which can be used for fitness apps and other applications. It allows the main CPU to snooze while it tracks the motion of the phone, through the accelerometer, gyrometer and compass.
That means the phone will know when you're jogging, and can take that information and store it without needing to drain the battery by having the main CPU chugging away.