geocalc

(not sure where the "phoenix sockets" fit into it) 1/ So I guess you're saying one process/GenServer per device, communicating with it. 2/ Use a Registry[0] to store the process names (based on the device id or whatever) to abstract them from their PID. 3/ Have another GenServer (let's call it CoordStore) storing a map of "process_name -> lat/long" (with the related processes sending updates of the coordinates to it) 4/ Use Presence[1] to keep track of the devices and remove them from the CoordStore when needed. 5/ When you have an anomaly on one device ask CoordStore for the nearby devices/processes (using maybe [2]) and ask each one (thanks to the Registry) to run the check. 6/ Done? (sure you can do a barebone version without the Registry or Presence but where's the fun in that?) [0] https://hexdocs.pm/elixir/1.14.3/Registry.html [1]

simple solution: store the geohashes and compare prefixes, each prefix length is equivalent to a distance. https://en.wikipedia.org/wiki/Geohash#Digits_and_precision_i... you can use this pure Elixir library https://hex.pm/packages/geohash or this NIF that wraps a much faster C library https://hex.pm/packages/geohash_nif or use one of the many geo libraries, like this one https://github.com/yltsrc/geocalc