I want to quickly share my solution for fridge temperature measurement. This is quite helpful to observe temperature changes and e.g. adapt the fridge settings. According to the German Verbraucherzentrale the fridge should operate at 7°C and the freezer at -18°C. For more details also see https://en.wikipedia.org/wiki/Refrigerator#Temperature_zones_and_ratings
My solution ends in this Basic UI view:
It is based on a Sonoff Basic and two DS18B20 sensors. I will not go into configuration details now, because all of this has already been discussed in other places. See:
I chose this solution at the time because (1) I had a Sonoff lying around and (2) it was a quite cheap and quickly set up solution. The big disadvantage is of course the need for an external power supply. How I solved this issue can be seen in the pictures below. In the fridge part I was able to go through the “dripping hole” in the back, in the freezer part I had to go through the door insulation. With proper preparation this method seems to work without issues or leakage.
Sonoff Basic Solution Pictures
Wireless and Battery-powered Solutions
The solution above is fun but what you really want is a battery-powered radio transmitting device with a temperature sensor.
One especially clever solution I’d go for nowadays is to abuse the Xiaomi Mi Flora Plant Sensor. Yes it’s supposed to gather data from a plant but the temperature (and light) sensor also work without being stuck in soil See here for more: Xiaomi Mi Flora Plant Sensor MQTT Client/Daemon
openHAB Rule for Temperature Summary
A simple rule is responsible for the Basic UI Sitemap view as seen above:
rule "Fridge Summary" when Item Kitchen_Fridge_TempCooling changed or Item Kitchen_Fridge_TempFreezer changed then Kitchen_Fridge_TempSummary.postUpdate( String::format("%s °C / %s °C", Kitchen_Fridge_TempCooling.state, Kitchen_Fridge_TempFreezer.state ) ) end