An innovation:
After several mechanical fridge thermostats failing over the years, I have replaced it with my own IoS controller out of general spite. (Usual rules apply: homebrew hardware, homebrew code, runs locally with no Devil's Radio or cloudy nonsense, isolate from mains before removing cover).
I've been tweaking parameters over the last week or so, and I think I've worked the most egregious bugs out of it (the thermostat set itself to NAN°C the other night, which was amusing).
Other than shiny monitoring and kicking up a fuss if someone doesn't close the door properly, the main benefit seems to be that the control loop can be much tighter, with less drastic swings in temperature. Which, in spite of making an effort to keep the freezer temperature vaguely sane (the old thermostat purely operated on the fridge temperature) and therefore keeping the average fridge temperature a bit lower, seems to result in a modest energy saving, presumably because the compressor isn't chugging away against diminishing returns to get the temperature low enough to switch off. (It's also saving about 3 watts overall by not constantly heating the thermostat with a power resistor.)
I'm also expecting vastly improved long-term stability against weather changes, because it's measuring the absolute temperature in degrees
SCIENCE with digital band-gap wossnames, not tweaking a springamathing against a bimetallic strip with a knob calibrated in whatever the refrigeration equivalent of gas marks is, which gets knocked every time barakta puts the sweet chilli sauce back on the top shelf.
(New controller put into operation on the 10th)
The other thing, which I did strictly as an experiment (our electricity tariff is a flat rate) was to see if adjusting the setpoint of the thermostat according to the real-time price of electrons
[1] (=> the load on the grid) was practical. It seems to work reasonably well, cooling down by an extra couple of degrees overnight and in the early afternoon, so it can keep the compressor mostly off and allow the temperature to rise slightly during peak times, maintaining a reasonable average temperature...
(Graph from the controller itself: The lines are hopefully self-explanatory. The shaded blue areas are when the compressor is running. The blue dots at the top are the fridge door being opened, and the green dots are fetching electricity price data. There would be red dots if someone had opened the freezer.)
A follow on from this, since I'd included a power monitor, was the ability to switch off automatically if the supply voltage drops too low. Because the students are back and the local substation needs all the help it can get.
In summary: Mechanical thermostats are rubbish. There's at least one good reason to connect your fridge to the internet. No I wouldn't buy one that did.
[1] Obtained from the Octopus API for one of the Agile tariffs.