On linux boxes you can place certain wireless NICs into monitor mode which will let them listen to all wireless traffic and with that you can print all wireless routers, cellphones, computers, anything that is broadcasting a 2.4gHz a, b, g, n wireless signal the NIC sees without trying to make connections to it.
I've looked for a solid three weeks and I haven't been able to find anything. Is the functionality I'm looking for outside of the capabilities of an ESP8266 ?