I'm struggling with a device which measures specific gravity,
temperature and battery charge - for wine making/brewing. It runs on
tiny battery and every so often wakes up, takes an sg measurement etc.,
connects to my LAN and supposedly sends the data collected to a
website, maybe every 15mins. There are a few such sites I can use for
this, but I'm struggling to get any of them working, or confirm the
data is being sent to them.

My two routers log connected devices, but the device showing up in the
lists are quite rare, because it only connects for a couple of seconds.
How can I be sure the device is managing to connect, how can I check if
it is trying to relay the data?