For a few days ago I thought about a different way to track presence, for people(friends in my case) that’s not even on my wifi. By using a ESP8266 in station mode sniffing for nearby smartphones, then posting them to my webserver which hash them and post them to my sql database.
Friend’s smartphones sends mac -> ESP8266 -> Webserver -> inserting( hashed(mac address) ) -> MySQL database.
My plan is to make a component, which loop “known_devices.yaml” and makes a HTTP_GET request with the mac address to the my webserver like: “htttp://example.com/last_active.php?mac=xx:xx:xx:xx:xx:xx”. The server then either returns TRUE or FALSE depending on whether the mac address have been detected within last 5 min or not.
The component then change the state of the device accordingly.
I haven’t make any custom components so fare, and pretty lost where to start, but I do have lots of experience with python. How can I do this using Home Assistant, maybe just as a rough coding example? Could be awesome to make this work, and have yet another method to check for user presence 
If anyone would be interested in the code for the php code run by the webserver and the ESP8266 sniffing code as well as the database table. I’ll happily make a clean version and share it