1. A system for detecting motion, the system comprising:a receiver at a first wireless communication device capable of wirelessly communicating with a second wireless communication device, the first wireless communication device configured to:
receive from the second wireless communication device via two or more subcarriers a first packet and a channel correlation for the first packet across the two or more subcarriers; and
control circuitry configured to:
estimate a channel energy difference for the receiver based on the channel correlation for the first packet; and
make a motion detection decision based on the estimated channel energy difference.