[centrinoblue]

I dabbled in designing a cooler/freezer monitoring setup for a local farmer not too long ago.

The 2 biggest constraints I found were power and communication from within the freezer.

One promising approach was - a BLE enabled temp. sensor beacon with a coin lion battery - a nearby externally mounted unit (RaspberryPi) plugged into a wall socket as a relay - a small central 'black box' SSD/Wifi/router ground-station to collect, store and push the data to the internet

The biggest question was whether the beacon signal could get through the freezer walls. If not then I was going to look into the idea of some super flat cable to enable a wired sensor connection without compromising the freezer seal (like a meat thermometer in an oven)

[manyxcxi]

Depending on the freezer, putting a hole somewhere and sealing it up really well is just as good as the walls and insulation that were in there before. I did this to a chest freezer that wasn't terribly expensive and I haven't ever noticed that the outside of the hole is any cooler than surrounding areas, nor did I notice that it had to work any harder to keep it cool.

That being said, I didn't exactly exhaustively detail the before and after performance of the freezer either. I used the smallest drill bit possible that would let me get a probe in there and everything else is external of the freezer down by the compressor motor where there is a lot of extra room- and input power to tap in to.

[centrinoblue]

I was evaluating designs from a potential commercial opportunity perspective so keeping things non-invasive was considered a constraint for ease of use and to avoid warranty/liability risk.

[manyxcxi]

Well then that makes a lot of sense for not wanting to put holes in it.