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: