I have had an Iris v2 contact sensor (not the magnet) in our freezer reporting temperature for the last year and while it has said the battery is at 37% for as long as I can remember it's still working however make sure you use something like @bptworld's Device Watchdog so you know if the sensor stops reporting.
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If you can find the original SmartThings multi sensor, the one that uses 2 AAAA batteries they seem to do very good in freezing temperatures. I have one in my freezer and after 22 months the battery is still at 78%. In fact these original sensors have more longevity than any other sensor I've bought since.
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I use Iris V1 contact sensors inside of my refrigerator and both freezers to monitor the temperature and the doors. You have to get creative setting them up with the magnets to monitor the door opening and closing but they work. The Iris sensors use CR2 batteries and work fine in the freezers for months and although they read ~50% battery levels because of the cold temperature they last as long as they do on any other door or window. Devices that use button type batteries will not cut it.
I tried a Xiaomi temp sensor in the freezer. Lasted a few weeks but then failed. Works fine in the fridge but the freezer is just too cold. Best to use a contact sensor on the door I think.
Our fridge has french doors and they were constantly getting left open (close one door, the other bounces half an inch open). I just stuck contact sensors on the outside of the doors and positioned the magnet right at that point where it shows close when the doors are completely closed. This has been working for us for a couple years now.
If the door is left open for more than 2 minutes, all the lights in the kitchen turn red until someone closes the door. The fridge has its own high temp alarm so I don't need to worry about temp.
thanks for the idea..thats awesome.
I set up an Alert in HSM..that seems to be working so far.
- I have the contact sensor mounted outside.....finicky to position properly but managed to get it to work.
- Set up an alert that is triggered after 2 mins....i figure that enough time for even my teen agers to open...find the ice cream, ponder if they really want ice cream.....put back the one cream and grab a popsicle...then close the door.......MAYBE need to set that to 3 mins:)
- After 3 mins - HSM triggers the alarm and a notification is sent to my phone via pushover.
I like the light options you note though. Apparently HSM has something similar but when i tried to "flash" a light upon alarm it didn't work. might have to try a different light...maybe it doesnt like a dimmer that i selected.
I was able to get the contact sensor inside the door to work to give me temp too I don't think im going to use that as the main alarm but i do plan on setting up a push over notification on elevated temps. Last year when i set up Griddy electricity...i have an automatic command to should down my AC units when the price of electricity spikes....but for some reason IFTTT won't allow me to make a command to turn back on....which is really weird..as i can se tup the same off / resume commands in IFTTT if i select lights....just not my AC... Anyway so i don't come home to an extremely hot house - i set a push over notification if my house temp goes above 78....which usually means Griddy spiked, IFTTT shut down my Acs and i never noticed to turn back on.
Love HE options
Cheers
mac
You can get this with any contact sensor depending on the magnets used. Personally I use rare earth magnets instead of the little contact magnet boxes. Gives you a larger magnetic pole/field to work with, letting you trip the sensor from further away, and over a larger area, so if things shift over time or someone managed to bump into one they usually still work.
Even if the refrigerator/freezer door is closed, but the unit stops cooling, wouldn’t you want to know that?
If it’s not cooling and I don’t notice than I must not be eating anything, so I’ve got bigger problems 
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I still want to see the internal temp...hoping a contact sensor will last...but if i go through a few batteries...no big deal.
interesting.....you wouldn't have a link to where you buy them by any chance - would you
ebay all shapes sizes thicknesses and quantities. 
What about when you are at work, or away on vacation, etc? 
I work from home. So does my wife.
Vacation isn’t something anyone is going to have for some time.
I get your point of course. I got it when @jeubanks made it 17 posts ago, that’s why I “liked” his post. 
But I’ve never worried about such things. If I’m on vacation and the fridge stops working, I don’t need to ruin my vacation with a problem like that. I’ll deal with it when I get back.
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My last fridge evaporator became partially frozen - defrost heater was working but small leak at the input of the evaporator caused a freeze. Basically a slow death that I would have caught sooner had I been monitoring temperature. I can’t tell the difference if food is frozen at -10C or -18C.
I cant see any downside to monitoring the temp inside fhe freezer. I have the platform and the extra sensors.
I only lost the stuff in the door this time and was kicking myself for not having a contact sensor on the door to detect that it was left open. I imagine id be kicking myself if the freezer died and i didnt detect it,.....so for the little time it takes...why not. I doubt i’ll look at the temp frequently so i’ll just monitor for a few days then set a rule for something greater but still below freezing to set an alarm. Lights and outlet rules are convenient. potentially saving whats in my freezer...thats the real power of automation.
Cheers.
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OK. I have to agree. I need to get a sensor that works in the fridge.
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Not trying to convince anyone......just letting people how i'd feel if i had further problems.
Cheers
Home Depot and Lowes carry them if you live in the US.
Like @DementedDragon I have used them instead of the large magnet that comes with the sensor because they are too darn big. Example my mailbox where I put an Iris V2 contact under the box and use a small round rare earth magnet on the door.
John Rob.
I think i have the contact sorted for this application but you mention a good option.
Can you tell me what type of contact sensors you know of that accept an external inputs?
Thanks
Mac
