I’ll start:
I’m monitoring memory usage on my NixOS build server using the Linuxfabrik plugin. Nothing special on its own…
This service has a Dependency which disables checks as long as there’s an “ld” process (procs, crit=0). Useful as I know linking Linux is expensive and don’t want a notification every time… 
Its not that weird, but a customer once wanted to monitor if mails are being sent. For this they sent mails to an external mailbox, which had a redirect policy to send them all back to the company.
Hi.
A few years ago I helped a customer set up monitoring of beehives for sound
volume, weight and temperature (internal and external).
The sound gives an indication of how active the bees are, the temperature
should remain pretty constant (the bees do that themselves) and deviations are
a bad sign, and the weight is both a measure of how many bees are at home
(varies from day to night), and how much honey is in the hive (slower.
Antony.
I used to have a weather check with temperature thresholds. If it was too cold, I brought the chili plants inside; if it was too hot, I watered them more often.
Sadly the used WeatherAPI is not free anymore and I deactivated the check.
@moreamazingnick I have had pretty good experiences with Openweathermap API last year. I have not checked whether they are still free, but i am pretty sure.
you could also work with humidity sensors in the soil, right?
Thanks for this thread, I like the gist of it!
The most weird (or useless) thing I am currently monitoring is the distance to the next xkcd Geohash - xkcd 426, Geohashing Wiki - with a custom check plugin. So sometimes I wake up with an Icinga Notification urging me to make an adventure to some random place nearby.
my check stopped working at Tuesday, November 5, 2024, but I just deactivated it, and didn’t check by it stopped
A long time ago we monitored baby monitors for hospitals. Also pool chlorine levels for really big pools (local govt). One of the trickiest plugins we have in production listens to audio over ethernet multicast and decodes it, checking for stereo, silence, jitter etc, and even converts it to wav to listen to it if the checks fail.
Check if websites are properly displayed on raspberry pi mounted behind TVs.
This check is a thin wrapper around a watchdog that compares against a picture or a string in a rectangle and restarts the browser if the conditions aren’t met. The old version under X used VNC but now under wayland it just takes a screenshot.
Test robots build with Robot Framework and a custom listener I made that reports to Icinga2.