At first I thought along with others that they're probably relying on some combination of Bluetooth and Wifi. When I launch FireChat though, it tells me that to use the chatroom that does not require Internet, it only works "up to 210 feet." Well, that's interesting because Bluetooth LE should work up to over 300 feet. If we're talking about two users on the same WiFi, they should be able to chat for as far a distance as that WiFi network, which again should be greater than 210 feet, depending on the system. So, if they're using a combo of WiFi and Bluetooth, how do they end up with a shorter distance?