Just want ti know if temp exceeds X, get notified.
Looking for a working freezer temp sensor. I see many BT + gateway versions but would prefer to use something Someone already has in play vice finding a solution.
Iris/Smartthings contact sensors can go down to 0F as stated on the documentation. That should be where your freezer is set, so it may work. Never tried.
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The concern I would have is that the metal case of a freezer might make it difficult for a signal to get out. Better would be an external device with a probe that would sit inside. Unfortunately, I don't think such a device currently exists, but would be glad to be proved wrong. 
Iris contact sensors work great and will read well below zero. My preference is the v1 contact sensor but v2's work as well. I have one in all my freezers and refrigerator. You can use the magnet to tell you if it has been open too long also.
The newer Smarthings multi-sensor will not cut it. It uses a button battery and will peter out within a couple of weeks.
I have an Ecowitt battery sensor in my basement freezer (with steel panels...). The sensor gateway is on the first floor. The gateway is connected to my WIFI and sends data directly to my hubitat.
(ECOWITT GW1004 + temp/humidity sensor)
I had it for about 6 months and it is rock solid. It is replacing a similar device (same technology) I had for about 10 years before it failed. I was changing the batteries about once a year.
The humidity jumps happen when the freezer door is opened, even briefly.
Iris gen 2 in both freeers, I first thought I'd use one as the door open/close sensor and temp On our new downstairs freezer but being up right next to the seal it reads much higher than if it is in with the food so I added a spare one to just read temps, the upstairs freezer I couldn't get a sensor to stick for long since it was already at freezing when I went to add the sensor so that one has always just been used for temp and has been in the freezer for about 2 years on a single battery, even though the battery shows that it is low
.They seem to report temperatures approximately with every 2 degrees change or every hour Whichever comes first.
can you buy the iris gen 2 any more?
Yes on ebay and if you want the V1 sensors, I can connect you with someone that has tons of them new. @scunny
For the record the V1 sensors are of much higher quality. I have a ton of them myself but I am keeping them.
Fibaro smart implant FGBS-222 with a temp probe DS18B20 or the old version FGBS-001. Both can do multi sensors, think new does up six and the old one up to four. Great bit of kit and there are fully working community drivers. Also maybe Fibaro door & window sensor v1 with DS18B20 and also the sonoff with external temp probe as another option.
I've got plenty of V1 sensors available. Brand new, $5 each plus shipping.
I have the Iris v2 motion sensors, which also report temperature, in my two freezers and refrigerators. I use the native notification app to notify me when the temperature is above a certain level. Very easy to set up.
I was worried that the radio signal wouldn't penetrate through the refrigerator/freezer walls, but it does. I was also concerned about battery life, but after one year the batteries are still working.
You should be able to find Iris v2 motion sensors on ebay. They are great sensors.
I've also been using Iris V2 contact sensors in refrigerator and freezer compartments on ST and HE; batteries do usually last for a couple of years (though the battery levels reported are best ignored). I suspect that the bottoms of most refrigerated compartments are just plastic and insulation with just some metal bracing; probably why my sensors wound up routing through repeaters in the basement.
Ordered 4 v1 sensors on eBay for $20 shipped. Inspired to put in my refrigerator and freezer for fun. Thnx for the inspiration. 
Thanks for all the ideas, I’ll look into each and see which seems the best for my situation.
From what I saw on the web site, it looks like these are Z-Wave. No thanks.
I believe @iharyadi ‘s rock solid sensors can accept an external probe. Very affordable and reliable. Zigbee and functions as a repeater (Xiaomi compatible too).
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@SmartHomePrimer thanks for mentioning my module. I really appreciate it.
Let me get right into what I think my sensor can do in the context of monitoring freezer.
The sensor that I have been making here has Analog Input that you can connect to an Thermocouple probe through a module like below. BTW, they can be had much cheaper if you do not mind Ebay route. Below is just an example.
You will also need a probe like below.
Using the probe (some has long cable), you will have the electronics outside the freezer. I have written DTH to use it. There will be no coding on this path.
However, that was the only option about a year or so ago. Today, my module can accommodate serial port connection. You can go with Arduino route to read temperature sensors. The module will act as ThingShiled. With this route, you can use probe like below.
Which again can be had in Ebay for a lot less. An Arduino uno clone is also be gotten for a lot less. The only down side on this route, you may need to write a bit of code in Arduino side. But, you will be able to do a lot more. The above sensor only take one of your Arduino pin. There are a couple pins needed for Serial ports. You still have more than a handful of pins on the Arduino for other stuff. Perhaps adding contact (reed switch) to monitor the door.
One aspect of the module is the battery backup. Some member here use it to detect power outage. Perhaps, this is important for freezer. You may not have to wait until your freezer temperature rising to know that something is about to go wrong by monitoring the power line. The module is powered by DC and has battery backup. If you add an LIPO or LI-on battery and the hub has battery backup, you can add circuit to monitor the power to the DC or monitor the battery report. Later is slower but no code/hack is needed. You can act faster if you have something valuable there.
As @SmartHomePrimer say you will get a Zigbee Repeater with extended Radio (additional amplifier),
Thanks. Please give it a consideration. I am here as community member will help you any path you take.
br
Iman
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Has any used Iris V3 contact sensors (IL06) as temp probes in freezer/fridge?
Soo.. let me verify
DWS800 is V1
3320-L is V2
iL06-1 is V3
Correct?
That makes each for 10 on ebay without magnet's
V1 $28.99
V2 $49.90
V3 $42.90
Are V2 that much better? I really only need 4 temp sensors for fridge freezer... But I'm sure I'll find a place to use extra ones...
I use the Sonoff TH16 with a SI7021 temp/humidity sensor, why I like this is the sensor is the only part in the freezer. I have flashed this with tasmota and I am using @markus universal drivers. This driver also has presence which I also use to notify me if this does not report in. I also use notifications if the temperature rises above -5 degrees C. Currently it has been in the freezer for about 3 months and the freezer temp is -22.5 degrees C.
All I have done is stick the Sonoff TH16 on the wall just behind the freezer and run the sensor wire (it is a bit short) into the freezer through the magnetic seal. This runs off mains power so no battery to worry about.
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