After I cut over to a new wifi router I left my old one partially configured with no internet connection and mirroring everything to one of the LAN ports that goes to an un-numbered (no IP address, no IP egress) port on my main server where I can maniacally sniff their futile unrequited traffic at my leisure.

The idea is to some day make a per-gadget catalog of all the hostnames and addresses these things want to reach, but hopefully someone beat me to it already and you folks can let me know where to find it.