IPhone M7 chip counts your steps even after the battery dies

When the M7 chip was first announced, there was much speculation as to why it was a separate chip rather than part of the main CPU.

A fair number of people were reasoning it could suggest it would be used in some other unannounced device (such as a watch etc).

While that's still possible of course, this is a much simpler explanation for the decision to have it as a standalone chip.