Source: ChiplocoThe iPhone 5S didn't bring a lot of new features, as you'd expect from an S upgrade. But like always, Apple did introduce cutting edge silicon that powers the phone. This time, along with the A7 chipset, we got the M7 motion tracking chipset as well. As the name suggests, this dedicated chipset is there to track the phone's motion which can then be used in a variety of different apps such as steps counter. But if this redditor's post is to be believed, your iPhone 5S maybe tracking your motion even when it's powered off.