How to measure the distance covered by iphone during free fall?

Question

During the free fall the iphone is supposed to send acceleration values as 0 on all the three axis. So how to detect the distance covered by the iphone?

Answer 1

Also keep in mind that the phone is VERY likely to be tumbling in any sort of falling scenario. As the phone's profile changes, the drag will change, and the accelerometer will NOT be reading zero.