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.)
I doubt you'd be able to get a signal through from inside the fridge. I made a Home Assistant "food safety" dashboard and alerts. I found two challenges:
* 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.
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.
The YoLink system works great! I was able to spot an issue causing my chest freezer to very slowly increase in temp (roughly -10 to +10 F in a month) and move the contents before losing the food. Across 5 temperature sensors, I've needed to replace batteries on 2 in 16 months.
There are loads of 'put them in the fridge/freezer' temp sensors out there, made just for this. I did buy lithium AA batteries (which work down to -40C even) for the sensor end.
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)
I saw a few that were wired with cords that seemed more intrusive than the telephone cord I tried, so I went my own way. And most of them didn't seem to be something I could connect to Home Assistant.
Well amazon has endless examples of wireless working fine. However, as I said, you get more flexibility with your own solution (like using Home Assistant)
My z-wave temperature sensor works inside my refrigerator. It's a stainless steel refrigerator with no window or icemaker in the door. Not sure how the signal gets out but it works.
Stainless is not a very good conductor. If it were aluminum or copper there’d be a problem but you can literally bury a bluetooth transmitter in a 16-gauge steel box with very little attenuation. I’ve done so at work.
Good news for you, their local hub is available and I currently have fridge and freezer (and a few other sensors) hooked up to home assistant via it right now.
