content: WiFi backscatter for dummies. Wifi backscatter sound complicated but in reality it is not. In it simplest way you can visualize it like this: Now your 500W light source has maybe 2500 lux brightness that gets received at the light detector via direct and reflected light. That 500W light source also gives enough power to a solar cell that is powering your Kindle e-reader.  The Kindle can now receive information from the 500W light source by varying the brightness just like a normal wifi signal. And because your separated light detector also receives the same variation and information by the light source how it changed brightness via normal wifi signal, it knows the signal base line. Anything that deviates from that predicted base line must come from a passive wifi device.  The big finale is this: The kindle changes its reflective screen to dark, reflective, dark, reflective,..... influencing the brightness received on the light detector. The power required to change the Kindle screen is maybe 0.1W based on the data it must transmit is maybe 0.1W which it gets from its solar panel lit by the 500W transmitter.  WiFi backscatter PDF: https://homes.cs.washington.edu/~gshyam/Papers/wifibackscatter.pdf Note: In the example a TV screen would of course mess up the signal, but in the real case it is a radio signal, so a electronic shielded TV would be silent enough not to interfere.