Might as well add bluetooth to the list if you include WiFi. https://en.wikipedia.org/wiki/Bluetooth_low_energy#Proximity_sensing https://en.wikipedia.org/wiki

Might as well add bluetooth to the list if you include WiFi. https://en.wikipedia.org/wiki/Bluetooth_low_energy#Proximity_sensing https://en.wikipedia.org/wiki/Bluetooth_low_energy#Proximity...