Open/Closed Sensor with EXTERNAL temperature probe

I'd like to retrofit my old SubZero refrigerator and freezer with door and temperature alarms.

Lots of open/closed sensors available that would work perfectly. Its the temperature monitoring bit that is more challenging. I've tried a few different temperature sensors inside the units, but range is terrible (obviously) and battery life is bad in the fridge and dismal in the freezer. So, a device that uses an external temperature probe would be better, won't have range or battery problems.

The question is whether I can find an all in one? An open/closed door/window sensor that you can also hook an ext temperature probe to. Anyone found one?

I currently use the Fibaro FGK-101's with an external DS18B820 probe, but I don't think they are available anymore. I'm also interested in finding replacements for these if anyone knows.

FYI, the new aeotec door/window sensor 7 pro looks almost identical to the Fibaros, got one, but turns out the external connection on these appear to be a dry contact only.

I have two freezers. I am monitoring the temperature of one with an older Smartthings multisensor. The battery life indicator is wonky. It shows 1%, but the sensor is still reporting in to the hub. The temperature seems to be accurte.

The second freezer is being monitored by a Hue motion sensor. The PIR part failed, but the temperature still works, so I put it in the freezer. In this case, the battery is showing 100% with new batteries and the temperature is being reported regularly.

The problem with using a sensor outside of the freezer with a probe inside is that the connecting wire will prevent the freezer from sealing properly. That may or may not be important to you.

I'd just drill a hole and seal up the path for the wire.

I am not sure how the SubZero freezers are designed, but in many freezers, the outer walls of the freezer contain the evaporator coils that allow heat to be released to the enviroment. If you drill through one of the coils, you will lose your refrigerant. So be careful.


Never built one before, but it might be a good idea. In particular, I wonder if a single arduino could handle both a fridge and the freezer? Or would I be building an arduino for every door/compartment?

You can put multiple DS18B20 sensors on a single Arduino board using one wire library.

single arduino, and multiple sensors (essentially one per pin). you can get something like the nodeMCU and integrate it into HE using [Release] HubDuino v1.1.9 - Hubitat to Arduino / ESP8266 / ESP32 / ThingShield Integration (ST_Anything)

I did this back in 2015 to monitor my garage fridge. The ThingShield is no longer available but there are other options like @haas’s board. Here was my write up.

I have since replaced this with Iris V2 contact sensors in both freezer and fridge. Batteries last a good 9 months. I needed the ThingShield for another project.

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