On our most recent IoT Podcast episode, we shared a question from our voicemail hotline about temperature sensors. Johnathan called in and asked about wireless sensor tags that can monitor temps in a freezer or outside. This is a fairly common question we get, with regards to people wanting alerts if freezer temps start to rise, indicating some power or mechanical issue.
Using these sensors in a freezer or a refrigerator adds a challenge that outdoor usage doesn’t. The way these appliances are built, they’re really good at blocking wireless signals. As a result, you’re probably best off with a wireless sensor that communicates with some internet-connected bridge or hub. And you’ll want that bridge or hub close to the appliance because even if wireless signals can “escape” the freezer, they won’t go far.
Many of these sensors use Bluetooth to send data because it’s more power-efficient than Wi-Fi, for example and can run on batteries. That also can limit the range of data communications. Additionally, most Bluetooth sensors only connect to a phone for data and alerts. That means remote monitoring information is only viewable when your phone is within range of the sensor, which probably isn’t ideal for what Johnathan is looking to do.
On the other hand, sensors that use some type of proprietary network over unlicensed spectrum typically do have a hub device, which gets the sensor data on to the internet, typically over Wi-Fi, to support remote alerts and monitoring.
The first option worth considering is a Bluetooth sensor from Tempi.fi, which costs $50.
It measures temperature and humidity every minute and can send that data to your phone. It can also store up to 22 days of sensor data locally. Just remember that the data synchronization is only when your phone is within the very limited range in this case. However, the company says it is working on a Wi-Fi gateway to make the sensor data available away from home.
If you can’t wait for Tempi.fi to offer their Wi-Fi gateway, there’s another option available now, although you’ll spend a little more for it.
A company called CAO Gadgets, based in California sells a range of wireless sensors including one that measures movement, temperature, and humidity for $29. Instead of Bluetooth, these use 433MHz airwaves, which are unlicensed and can carry data farther than Bluetooth. However, there is no local storage on this sensor.
You can add a $39 Ethernet Tag Manager, which gets the sensor data on to the internet so it’s viewable remotely in a phone app.
This also adds support for Amazon Alexa, Google Home, and IFTTT for automations and it can receive data from up to 40 sensors. Without the Tag Manager, you’ll only get alerts and data when your phone is within range, so if you want remote access you’ll need to buy this accessory.
To hear Johnathan’s question in full, as well as our discussion, tune in to the IoT Podcast below:
Kevin
You need to reach out to Shelly. Their CEO has been running their battery operated WiFi sensor in his freezer for over a year. They do so many of the things you mention here but you never look into them – they’re on Facebook – their CEO is on there several hours a day talking to us. Look up Shelly Support Group English and tell them who you are, they’ll be glad to talk to you.
Thank you for this! I was so mad when I accidentally left our basement freezer door slightly ajar one day and everything in the freezer was soft when I found it. I thought I looked into this a few years ago and was told it would be difficult due to the thickness of the fridge walls not allowing wireless through. I am glad someone made the 433 Mhz tag… that’s perfect! I will no longer have to suffer with refrozen popsicles shaped like puddles! 🙂
LoRaWAN is the answer. Costing more to be sure, you can setup a indoor gateway at your home, instantly turrning it into a smart home, and have a range of devices and sensors doing various things such as measuring temperature, humidity, luminocity, motion, leak detection and yes – even measure temperature at freezer. Sky’s the limit with LoRaWAN. Operates on 902-915Mhz and the market is flooded with offers
Rude and unhelpful customer support.
I am an early backer of the Sensor Tags from CAO Gadgets, LLC. The tags and hubs were very expensive (hundreds of dollars) and, due to technical issues with their technology, they never worked as designed for my application.
Recently, I have tried to revive these tags for use in a less demanding application (with hub just feet away from the tags for better communication and setting things up in the most optimal way to overcome the technology limitations).
In the course of doing so, I ran into several bugs and I had several questions about compatibility with CAO Gadgets new tags and hubs.
Their support department was dismissive and rude from the get-go but I persisted with my questions in an attempt to get a meaningful answer. Despite ensuring that my tone and questions were polite and relevant, I received the following answer from their support department:
“Are you angry? Find something else to do.”
This after simply asking if there were any release notes or known limitations in the previous versions of the tags so that I could design a use case that overcame these limitations.
For what it’s worth, I had similar experiences with CAO Gadgets back when I first purchased the tags. I would appear that either the same support staff are still working there or that their attitude toward customers has not changed.
It is a shame that a product whose technology shows such promise and utility is hobbled by a company who does not stand behind their products and who are abusive to their customers.
Towards Chris Pauly’s problem, I have a Samsung Smartthings hub and purchased a couple of their multipurpose sensors. I placed them on the top of the freezer and ice maker doors (which are in my garage) and setup automation to send me and my wife text messages if the door is open longer than 5 minutes. That works OK, but they often lose connectivity with the hub and I don’t get any notification and, of course, notice it when I go to the freezer and find everything melted… it’s still a work in progress.
The problem I found placing sensors inside the freezer is that connectivity is even more sketchy (as Kevin mentions in this article) but even more of a problem is that the extreme cold temperatures make the battery life extremely short. Naturally, these mini-sensors don’t use batteries that come in a rechargeable form factor. I expect that the CAO gadgets would have similar issues (plus Peter’s shocking review of their customer service certainly isn’t an endorsement).
The nice thing about using a hub is that it has a some amount of automation capability built-in rather than relying on IFTTT who has now moved to a rather costly subscription model for the ability to code more than 3 routines.
Hi Bob! I purchased that CAO gadgets unit. It works remarkably well and you can tune how often it pings, so the battery also lasts quite a long time (about 5-6 months.. CR2032 I think). When the low battery notifications started, I ignored them like I do with most of my devices. However within that month the unit died. I didn’t notice since I normally only know it’s still running when it triggers a high/low temperature threshold (which actually happens more often than I realized even for my freezer when the doors are tightly closed, but that’s another story). When I finally noticed that my tag stopped sending temp alerts, I noticed the unit has been dead for a couple weeks. I went about changing the battery. These units are fairly low-level spec… so letting the batteries die for too long and not replacing the battery correctly bricked the tag. I tried using some low-level jumper pin shorting to recover it, but either didn’t follow the instructions correctly or let too much humidity short the unit… it was dead-dead. I emailed their support and it took a little while but they had me try a few things that didn’t work and ended up sending me an RMA pre-paid shipping label and I sent it back to them to fix. They either fixed it or replaced it within 10 days and I had it back.
So I’ve been generally pleased with it. The software/apps for it crash a lot and can be confusing to use, but the notifications is what I wanted it for and it does seem to do that when triggered. Overall I’m very happy and would recommend their devices.
Ideally you would have a unit that attached magnetically to the freezer with a wired sensor inside the freezer using a flat wire to minimize air leakage. Thus whatever wireless format you choose, the signal will not be attenuated and the batteries won’t be affected by the cold.
Wouldn’t it be possible to use an old cell phone as a “hub” and have it send wifi notifications to your phone?