Learned my lesson after a trip last week… I have sensors for nearly everything, but somehow totally forgot about the Fridge / Freezer.
A power outage made my fridge lose it’s mind and turn off cooling, even after it powered back up. Unplug / replug seems to have fixed it, but all the food was spoiled when we got home. Simple $10 temperature sensor could have saved everything!
If you live in a climate in which you need to winterize your outdoor faucets (e.g. by shutting a valve in your basement, crawlspace, or garage) a temperature sensor on the warm side of the valve can save you from a flood.
I had to replace the garage door opener one winter and failed to notice a new quarter inch gap at the bottom of the garage door. Combine that with a cold snap and the garage dropped below freezing for long enough to burst pipes.
Fortunately I had a Shelley flood sensor on the floor so I was alerted fairly early and was able to avoid serious damage, but had I been paying attention to the pipes themselves I could have avoided a plumber call-out on Christmas Eve!