Fridge / Freezer temperature monitoring / sensing

Right in the middle of self-isolating for the virus (just being extremely careful), my fridge/freezer decided to die on me - fuller than it’s ever been! Just had an appliance guy out and he’s confident that he’s fixed it (new relay) but … I want to monitor temps from now on. I’ve searched this forum and there are a few old threads on the topic, but nothing recent that I can find.

So - any recommended temperature sensors that work in the freezer? I’ve currently put a Samsung motion sensor (which also reads temp) and an Aeotec Multi-Sensor 6 in there to see how they go. The Samsung motion sensor is giving a reading of -3F, which seems accurate (but took a LONG time to get down there) and the MS-6 is also reading close to 0F, which is not bad (and it got down to that temp much faster. But - the Samsung motion sensor went from 100% battery reading to 30% battery reading in just 1 hour (presumably because temperature is changing the chemistry).

Anyway - what’s the current ‘best choice’ for something that can go in the freezer and operate at circa -10F?

It also occurred to me - There is a bulb in the fridge; can one use an adapter to ‘tap into’ the power, and still have the bulb work? That way, my MS-6 can be USB-powered through an adapter.

1 Like

Batteries don’t like freezing temperatures. That being said, I’ve had good luck with my Frankenstein temperature sensor. I took the earlier generation SmartThings door sensor, got rid of the button battery that dies ultra fast, and soldered on a 2xAA battery pack. It’s ugly, but the batteries have been lasting me around 13-14 months. The sensor just sits on a shelf off to the side on one of the shelves.

I have webcore monitoring the temperatures with some pretty aggressive alerting. I also have a webcore piston that will alert me if no temperature updates are received after a few hours. That second piston is useful since the battery percentage isn’t particularly useful, even before Frankensteining different batteries.

I have the same Frankenstein. I have an ST motion sensor in a ziplock bag drapped over the door of the chest freezer and placed inside. There are 2 leads soldered to a pack of AA that hang outside the freezer so the batteries are never cold. Reads -20 C and I have a piston set up for the alarm.

Alkaline batteries are range bound in temperatures. Lithium batteries perform quite well even upto -20C. You can find the charts and a write up about battery chemistry v/s performance here:

You can get AAA and AA Lithium 1.5v batteries from Energizer on Amazon. If you’re operating at low temperature or high load, these batteries will outperform alkaline batteries on a $/mah delivered basis over the life of the battery.

My experience hasn’t really been that great with lithium AA batteries. I tried using them around 5 years ago in a “dumb” freezer temperature sensor and it wasn’t all that much different than alkaline.

I can get a 48 pack of alkaline AA batteries for around $14. An 8 pack of lithium AA batteries are around $13. 5x the price per battery, and I doubt it would be 5x the performance at nearly the bottom end of the supported temperatures.

1 Like

Update - I’ve been monitoring my new fridge/freezer, as well as the old one (repaired, sitting in the garage for now, as an aux. device). I’m using a Samsung water sensor (which also reports temperature) that has a ‘CR2’ lithium battery, and it’s doing quite well so far - it was at battery level 82% when I put it in the freezer, and it’s now at 55%. I get very good readings every 1 degree of change and/or every 5 minutes. I really need to return it to its original purpose, but for now it’s a good test.

I’m also using a Samsung motion sensor that has a ‘CR2477’ lithium battery (button) in the other freezer. This guy is also giving me good, accurate-looking readings every 1 degree of change and/or every few minutes. But the battery on this guy went from 90% down to 1% within minutes of going in the freezer; it has stayed at 1% ever since, and continues to work fine (~12 days so far).

I’ve also got an Aeotec Multisensor 6, with 2x CR123A Lithium batteries, in the fridge compartment of the old fridge. Obviously, nowhere near as nasty as the freezer environment; he’s performing fine, and reporting temps every 10 minutes regardless of temp change. Battery hasn’t dropped below 100% yet.

Finally, I’ve got another Samsung Motion Sensor (newer model, with a CR2 Lithium battery) in the fridge compartment of the new fridge. He’s also reporting very frequently and accurately and the battery hasn’t dropped below 100%.

So I’ll see how long the freezer-based Motion Sensor and Water Sensor last. At circa $18, maybe the water sensor is a good solution (Samsung GP-U999SJVLCAA Smart Things Water Leak Sensor).

1 Like

Any updates on this experiment? I’m trying to find best freezer solution as well.
I am wondering if a contact/temperature sensor that takes the larger (vs CR2) CR123a lithium battery would be best of all (vs frankensteining an external battery source.)

My opinion is that the actual temperature probe should be external ie. connected to the zigbee/zwave/cloud device by cable. It should also be natively supported by ST. There is not too many such devices, if any. One choice is Fibaro Smart Implant with external sensor but that is a bit pricey and may need some custom DH etc.
My choice is diy Konnected device with temp. (and hum.) sensor. The HW is very cheap and Konnected cloud is free (hopefully forever) and it is supported by ST. The device is powered by USB power supply and only the sensor is inside… whatever. I’m using it currently in sauna (high temperatures). Next I do the freezer (low temp), then outside (high/low/wet) and maybe sometime the pool (immersed).