UW engineers achieve Wi-Fi at 10,000 times lower power
The low-power devices don't actually generate any signal at all thus don't have to pay that expensive power cost.  Instead a passive antenna is modulated to reflect or absorb ambient signal, the reflected signal conforms to traditional 802.11 packets.  The ambient signals are created by a relatively high-powered device that is plugged into wall power.Here is a 2 minute video showing an early prototype of their work from 2014:https://www.youtube.com/watch?v=snZWgAZqo2c