A battery powered gadget, wakes up every 15 minutes, logs into my
router just long enough to send a batch of data to a website and then
goes back to sleep. The gadget in operation, is inaccessible, but
flashes an LED on the gadget when it transmits. Waiting 15 minutes for
a flash of a few milliseconds isn't an easy solution anyway.

My router, which it connects to, only shows it in its list of attached
devices if I happen to log into my router at just the right instant. To
add to the problem of confirming it is working, the website is
sometimes just not available.

Is there any way I can confirm the gadget is actually working and
sending the data batches?