Test of MyHarvia Smart Sauna Sensor Wifi – The Next Generation Thermometer
Harvia has just remarkably expanded its digital product ecosystem. In April 2026, they launched MyHarvia Smart Sauna Sensor Wifi, an independent device for monitoring your sauna temperature over the internet. It builds upon their fresh Fenix controller and the second-generation MyHarvia 2 mobile application. It monitors sauna room temperature, humidity, and motion to guide users in effective use of their sauna.
Saunologia got the opportunity to test the device already before the launch. I report all the fun I had while testing – despite almost setting the unit on fire! I found it an easy and affordable way to get detailed insights into your sauna environment that outperforms benchmark devices. I am also happy to report that the Harvia team resolved several software bugs I discovered prior to launch, building confidence that the device will be valuable in the years to come. The new model has been for sale since January 2026 in Europe, and now in North America.
What is MyHarvia Smart Sauna Sensor Wifi?
Harvia Smart Sauna Sensor Wifi is a device that measures the sauna room temperature, humidity, and human presence inside the sauna, and sends the information to the Internet via wi-fi. Sauna users can access the information via a mobile app, a web interface, or programmatically via an API.
The Sauna Sensor is offered as a stand-alone product, even though it uses the same MyHarvia 2 software as the new Harvia electric sauna heaters do. The device is sold individually, costing under 100€ and 100 USD. No subscription is required to access the data or use the mobile app, it’s free for the lifetime of the device. Harvia calls this Core tier functionality of MyHarvia 2.
The origins of Sauna Sensor
The product is one of the first digital products Harvia’s Head of Digital and Services Perttu Rönkkö has been developing since he joined the company in 2023.
“We wanted to develop a new device that makes it easy to connect any home sauna – including wood-burning saunas – to the internet. Measuring the sauna environment plays an important role in better understanding the long-term health benefits of sauna use, as people can easily observe whether they are getting a beneficial dose of heat. Secondly, this monitoring solution makes sauna heating easier and can increase users’ awareness of energy efficiency, helping households reduce energy consumption by the device simply notifying users when the sauna is ready,” Perttu explains to Saunologia.
For Harvia, the new MyHarvia Smart Sauna Sensor Wifi represents a pioneering device of its kind, and the company expects to release additional versions of the Sauna Sensor in the future. Perttu adds that a professional-grade sensor with a fixed power connection is already under development.
this monitoring solution makes sauna heating easier and can increase users’ awareness of energy efficiency
For this Saunologia test, I was using the sensor independently of a heater. I got an opportunity to test both a production (January 2026) and a pre-production unit (December 2025).
The physical device at a glance
Sauna Sensor is a simple, rounded black plastic shell. The design resembles a a round seashell, being wider (4”; 98 mm in diameter) and fairly flat (1”; 27 mm). The unit weighs 130 grams (4.5 oz), so it needs a sturdy wall fastening point. A small black screw is provided for this purpose, easy to apply within wooden sauna rooms. The sensor is intended to be hung on a wall, twenty centimetres (8”) or more below the ceiling.
The formidable-looking device houses a temperature sensor, a humidity sensor, and a movement sensor (PIR). Being a wireless device, it is battery-powered, using a custom-assembled battery designed to withstand high temperatures. The battery is initially disconnected using a plastic strip, and the user can replace it later. If the manufacturer’s promise of several years of operating time is any good, then the solution seems acceptable.
The reason this might be true is that the device has a smart standby function so that the sensor only activates and connects online when the sauna is warm. Otherwise, a custom and non-rechargeable battery easily becomes a headache, as with many other home smart IoT devices.
Other noteworthy details are the semi-open structure and the Bluetooth activation button found on the back of the device. In testing, the button worked as expected and you only need to press it once to get the device connected. The device is open on its sides, which is not immediately obvious. This enables the sensor to react more quickly to its environment, so you cannot submerge it in water, but it is protected against splashes.
MyHarvia 2 software for the MyHarvia Smart Sauna Sensor Wifi
MyHarvia 2 (Fenix) application was introduced in 2025 as a replacement for the first generation of Harvia’s mobile app. The new app is identical across iOS and Android platforms. The iOS app can be used on both iPhones and iPads, since there is no iPadOS-specific app. The app is only available on mobile devices, not on computers or in web browsers, although data is available in a different over the web. The app supports nine languages, including the main languages, and defaults to the device’s primary language.
The renewed app replicates the look and feel, unifying the Harvia control interface across Fenix devices. This is the preferable option for user interface design. Harvia has also been able to introduce all common features from the previous generation immediately with the launch of the new software, even if the new app is still under development. Luckily, the software received several updates during the test period, promising that issues will get fixed in the future, too.
Setting up MyHarvia Smart Sauna Sensor Wifi with MyHarvia 2
With ”smart” devices, the first and foremost challenge is usually getting the device set up. After this, robust devices usually don’t need much attention, so this step is crucial for usability.
To get things going, the MyHarvia 2 app must first be installed and a user account created for the new system. Existing credentials for older MyHarvia do not work with the latest software. Account registration uses a conventional email and password combination, not single sign-on via Apple, Google, Meta, or other identity providers.
The app asks for permission to send push notifications, which I recommend allowing to get the most out of its features. However, it should also ask for the precise location as this will be required to connect the sensor. Although the location is only needed when using the app, for me as a consumer, this feels unnecessary, since setup will fail unless you are co-located with the products, and the app should not really care where the setup occurs.
Once you’re in the app, you can add your new sensor device by allowing the app to use your location and discover nearby Bluetooth devices. The connection process is straightforward and should not pose difficulties for anyone who can remember the name and password of their wifi network. For me, it took about two minutes to set up the sensor as can be seen in the embedded video taken on an Android phone (note the flow has improved since I made the video). The flow for a sauna with a wood-burning heater is one step longer than for an electric heater.
The setup concludes by setting the default target sauna temperature. This setting is so crucial to the software’s function that it could come much earlier in the process. Luckily, you can adjust it later if needed. After completing the setup, you can mount the sensor on the sauna wall, and it will be ready to use!
Sauna Sensor in action
Sauna Sensor is a simple monitoring device, so when it works, it is unnoticeable. The unit itself has no display or power indicator, but the software comes alive when the threshold temperature of 40°C (104°F; or other user set value between 30 and 40°C) is exceeded.
The idea of the sensor is to track the heating and usage of the sauna until activity inside the sauna quiets down. The software attempts to learn how the sauna typically heats up and notify the user when the target temperature is achieved. This is where some people may get their first surprise.
If someone is accustomed to using an electric sauna heater’s external temperature sensor for regulating sauna (say, at 80°C; 176°F), they may be surprised to find that the temperature elsewhere in the sauna can be far from that. So, depending on how far from the external sensor (or old thermometer) the new sensor is placed, the actual sauna temperature might remain far lower than expected.
For the Sauna Sensor, this means you probably need to reduce the target temperature to match the sensor’s measured temperature. Once you get your temperature target calibrated, the Sauna Sensor becomes more useful.
Monitoring your sauna with MyHarvia 2 sauna app
MyHarvia 2 app has many more capabilities than the sauna sensor needs. This is because the app is also designed to work with Harvia Fenix heaters. So, for this review, I will focus on the key things that the Smart Sensor uses.
First and foremost, the device can trigger notifications in the MyHarvia 2 app to indicate when the sauna “is ready” or when it is “heating unusually slowly.” In the case of a wood-burning heater, the slow heating or even declining temperature can trigger an in-app warning to ”add more firewood”.
When you do open the app, you land on its main screen, which clearly displays the current sauna temperature, the target temperature, and possibly the remaining heating time. Additionally, the main screen displays a graph from the previous or current sauna session. The graph displays all recorded signals, temperature, relative humidity, and presence (motion inside the sauna). More history is available through the web dashboard.
I think Harvia has done a good job of laying out the key data on the main app screen. For people with normal vision, checking the app at a glance quickly provides all the information you need about what’s happening in your sauna. My only concern is the app’s accessibility, which is not up to the requirements of the current European legislation. While this is not unusual in the business, I believe that a wellness-oriented brand such as Harvia could quickly gain more goodwill among sauna users who, for example, don’t see well and would like a larger font size. Having an accessible sauna app might even improve the safety of sauna use for those with severe vision impairments. I think Harvia’s app team has proven itself agile enough to address this challenge once it sets its focus on it.
I used the sensor in association with heating a wood-burning sauna, too. The system learns to recognize the heating pattern of the wood stove and can adjust, for instance, by sending a notification to add more firewood. This sounds nice, however, I personally have not become dependent on this feature. There are two reasons. First, when the time is start preparing my sauna, I prefer tucking the mobile phone aside as I like to focus on the sauna while at it. Second, on Android, the delivery of notifications didn’t seem at the right time. I don’t think the problem lies with the app, it’s more an Android platform challenge as I’ve witnessed similar delays with other apps.
Web dashboard and further connectivity
All of the Sauna Sensor data is available on the Harvia web portal at https://harvia.io/, which uses the same login credentials as the app. This allows you to check the number of sauna sessions and their details. It also displays data recorded between active sauna sessions, allows you to change the sensor configuration, and much more!
The most useful setting hidden here is the “Wake up temperature.” If you use the sensor with a wood-burning heater – or your sauna cabin is cold to start with -, you will want to decrease the default temperature to the lowest setting, so the sensor wakes up earlier when the action happens. Given the non-linear heating curve for a wood-burning heater, there is more information to be gained before hitting the 40°C (105°F) threshold. If you had the sensor in a cold outdoor wood-burning sauna cabin, you might be through to your second batch of firewood before the default 40°C is even achieved!
I think Harvia has done a good job with the web portal, significantly enhancing the value of the measuring device by providing well-designed access to all the data. One of the features I especially appreciate is the visualization of the sauna heating curve, a unique idea in the domain.
If you’re still unsatisfied with data access after browsing Harvia.io, there’s also the programmatic access. For real data nerds, there are two APIs: GraphQL or REST which allow the same data to be accessed after authentication.
A heat shock test and a miraculous recovery!
Since I knew my sauna conditions would never push the sensor past its upper limit, I decided to try something else so we could all see if it really survives 130°C (over 260°F). So, I placed the unit inside an oven (a wood-burning masonry heater) and carefully waited, occasionally observing the oven’s built-in temperature reading.
What I didn’t remember is that the oven heats up from the bottom, but the temperature is measured from above. After this realization, I removed the sensor while the surface temperature in the oven was already above 160°C, and the plastics on MyHarvia Smart Sauna Sensor were deforming! If I had kept the unit inside much longer, there would probably have been more serious consequences.
After the device had cooled down, I examined the unit and found that, despite visible damage to the plastics, including the PIR sensor lens at the front, the sensor appeared to be intact. Also, the battery housing was warped, but opened without much effort. And miraculously, the device continued to work despite the damage, as before; even presence sensing still worked, which seemed miraculous given the visual damage. And it still works two months later. Impressive outcome and a heavy check mark for safety!
Benchmarking against competing products
MyHarvia Smart Sauna Sensor Wifi is the first consumer device in its very specific category. Previously, the Finnish company Saunasampo offered a similar Saunamonitor dashboard product for professional use, but it has not been widely adopted. So, the best comparison points are general-purpose sensor systems, such as Ruuvi or the Sensirion platform products.
Being a Finnish company, Ruuvi has been deployed in many saunas across the country in DIY digital thermometer setups, so it seems fair to compare it with the MyHarvia device. The basic RuuviTag is the most affordable, costing under 50€ per unit. It measures temperature and humidity and sends the data over a Bluetooth connection. The Bluetooth signal can be processed on Ruuvi’s mobile application (iOS or Android) or picked up by Ruuvi Gateway (200€). The gateway device can send the data to Ruuvi’s Cloud (subscription needed). This combination becomes much more expensive than Harvia’s sauna-only solution. The upside of Ruuvi is that the Bluetooth can be securely handled locally so you don’t need to send it to the internet, for example, if you have your own Home Assistant or similar service (not that you probably do, but…).
Besides total price, Harvia has some technical advantages over RuuviTag. The MyHarvia Smart Sauna Sensor Wifi is rated up to 130°C (266°F), which far exceeds regular sauna temperatures and even the range offered by most electric heaters. Ruuvi, on the other hand, is limited to well under 100°C, and its battery can fail quickly in high, but realistic sauna temperatures. While this can be compensated for by placement, Harvia is still more sauna-friendly.
The MyHarvia Smart Sauna Sensor Wifi has also been designed to catch rapid temperature changes, which are not a strength for Ruuvi. Although that can be remedied by modifying Ruuvi enclosure, its clear that Harvia has the upper hand.
I have been using Ruuvi, both RuuviTag and RuuviTag Pro for years, and plan to keep on using them, but I do enjoy the simplicity of Harvia’s overall product.
On behalf of RuuviTag, I must say they have turned out surprisingly robust in the years of sauna use I have subjected them to. The other advantage for Ruuvi is data frequency as with the app, you can receive data every couple of seconds. This has little practical value generally, but it might be crucial for sauna nerds such as myself. They are also smaller, so far, experimental work that calls for multiple sensors in a single sauna. Ruuvi is probably a better fit.
Edit 27th April, insertion:
Out of a public request, I am commenting on the relative validity of the competing sensors. In a test run with MyHarvia, Ruuvi tag, and Ruuvi Pro, all devices eventually reach a reported temperature within 1°C of each other (around 72 to 73°C). MyHarvia and Ruuvi tag get there side by side, Ruuvi Pro is the slowest of the three. So, the validity of the temperature measurements is comparable. Humidity is another deal. I originally omitted reporting anything about validity, as I didn’t really have very good standards. An issue with Ruuvis is that humidity measurements become increasingly unreliable over time. They can still reveal the presence and relative strength of löyly but inter-test reliability is poor. In my tests, I get convincing humidity variation, but the absolute figures are whatever. So I tend to trust Harvia’s number more, at least now that the unit is still fresh (well, the one that is).
Verdict: nice to know or actual value?
Here in Finland, people have an ambivalent relationship with sauna measurements and monitoring. Several people I know are opposed to even having a thermometer in the sauna, let alone more sophisticated sensing. Given that the Sauna Sensor acts like a remotely accessible thermometer, there will be people who will say it’s just nonsense.
But some folks have already been setting up their own smart home or professional sauna monitoring systems with generic solutions (that would be me, too). They can welcome this new product as a smooth solution for a long-standing problem. One that is truly designed to solve this problem well.
The people who are likely to get the most out of this sensor are those using an electric heater with integrated controls as well as professional sauna operators who need to monitor multiple saunas continuously. If Harvia continues to expand the Sauna Sensor product line, there may appear even more interesting devices. For example, if they create a 4G or 5G cellular radio version, it would increase the sensor’s versatility for wood-fired sauna cabins that are out of Wi-Fi range.
In the MyHarvia Smart Sauna Sensor Wifi, Harvia has packaged most essential sauna environment measures into a single device. The most notable omission is the carbon dioxide (CO2) level sensing. Its absence is understandable, as technically, energy and temperature requirements for CO2 monitoring are challenging. Adding more capabilities would easily hike the price, as the best comparable CO2 monitor I know (Aranet4 Home) costs more than double the Sauna Sensor. So, for what it offers, the price is very competitive.
Good value for money
The current sensor is selling for under 100€, or 100 USD if you’re in the US. It is relatively affordable in the category of sauna auxiliary products. Among IoT temperature and humidity sensors, it is a bit costly at the first glance; however, most of the simple thermometers are not Wi-Fi (or 4G!) enabled, instead communicating on Bluetooth or Zigbee to a hub device. That makes up a more complicated device setup and adds to the price. It’s also important to notice that the Harvia device is rated for exceptional environmental temperature, and the software is optimized for sauna use. Thus, the value for the price seems good.
The real question is how the device will prove itself over the long term. This means both the hardware surviving technically and the application’s continued availability to users in the years to come. For free, that is. And of course, how much value will users get out of sauna monitoring in the end, or will you get tired of it soon? But I guess many of us own scales even though we don’t constantly monitor our weight.
Overall, the biggest question marks this test, with all its positive findings, could not resolve is the promise of battery lifetime and actual reliability in sauna conditions. This is something only time and variable environments will tell. But fresh out of the box, this Harvia product seems to be one of the most innovative to emerge from Muurame in a long while!
Buy and learn more online:
https://www.harvia.com/en/products/SAM001W/myharvia-smart-sauna-sensor-wifi
In North America, the sensor can be purchased from several outlets, including Amazon.com:
https://www.amazon.com/dp/B0GPLDHRDX
This post was created in a commercial collaboration between Saunologia and Harvia.
