I plan on putting some LoRaWAN temp sensors in my fridges/freezers to alert me if the temp goes out of spec for very long. (As soon as YoLink has their Local Hub available and functioning with Home Assistant.)
* Connecting to the outside world. I didn't go wireless because a fridge/freezer cavity is basically a Faraday cage, because I didn't want to deal with replacing batteries, and because high humidity + low temp = wet, sad microcontroller. And even a "flat" 4-conductor telephone cord disturbed the magnetic seal enough that there was a noticeable gap. I ended up buying a 4-contact, 1mm pitch, 200mm flat flexible cable to run across the seal. I separated the contacts with a utility knife, soldering them to other cables on both sides. I also heatshrinked the conductors individually and the whole junction together for strain relief. Then I superglued it into place. And 4 conductors is enough for ground, supply voltage, and either TX/RX or 1-Wire+unused.
* Getting a reading that matches what foods actually experience rather than the air temperature. The latter fluctuates a lot more when you open/close the door or depending on what the defrost/compressor is doing. I ended up buying waterproof 1-Wire temperature sensors (elecrow sells them for $1.20 each + reasonable shipping), 4 oz plastic bottles, cable glands, and propylene glycol (relatively safe antifreeze, though I wouldn't chug it). I drilled holes in the lids for the glands to run the sensors in, then closed the bottles up while immersed in the solution. Cheap DIY buffered temperature probe.
I currently measure buffered temperature, air temperature, and humidity, but really only the buffered temperature matters.
My thoughts are, these things are special built, and only wake every few minutes or so to burst send. Batteries tend to last a couple of years (but with the lithium ones!), and I get beeeeps from the receiver if it dies.
(Not knocking your solution, it gives you more flexibility)
For the readings, I only really care about catching compressor failure within hours, as opposed to say, days, so for a freezer that's normally set to -18, I figure I'll just do something like "alert if temperature remains above -14 for >2 hours." Of my 4 fridges/freezers, only one has auto-defrost, so I guess I'll have to take that into account there.
In the freezers I also employ either the "freeze some ice cubes and put them in a baggy" or "freeze a small jar and put a coin on top" methods.
If you see the ice cubes have melted and refroze, then trouble. If the coin is not on the top of the jar -- same thing. Fail proof methods.