Guide
How do ultrasonic mist humidifiers work?
by Martin Jungfer
Measuring CO₂ – what meters can and cannot do
25.10.2023
Translation: Veronica Bielawski
There are CO₂ meters in every price range. And cheap ones aren’t necessarily useless. But expensive models are often more accurate and offer an expanded arsenal in the fight against bad air.
If there’s one thing the pandemic has taught us, hopefully it’s that viruses and bacteria especially accumulate indoors – and that the risk of infection is higher, especially when the air quality is poor. In other words, air with a high carbon dioxide content, or air that’s been breathed in and out of many pairs of lungs.
But how can you tell how good the air is in a room? Sure, you can often smell when the air is bad – just walk into a stuffy meeting room that’s been occupied for hours. But if you’re stuck in a meeting room yourself, chances are you won’t notice the air getting worse and worse. This is where CO₂ sensors come into play. I’ve tested a few over the past months.
The Sensirion: small but mighty
The Sensirion is the smallest meter I tested. It costs just under 60 francs or euros (as of October 2023) and is the size of my thumb. It runs on just 200 mA and connects to the power via USB. You can use the Sensirion sensor with any USB port – for example on your laptop or on a USB charging plug.
Technology-wise, the Sensirion is made of a relatively simple circuit board with an LED and an air quality sensor, the SCD41. Depending on the concentration of CO₂ measured in the room, the LED lights up as follows:
- Green between 400 and 1,000 ppm CO₂
- Yellow between 1,001 and 1,600 ppm
- Red at over 1,600 ppm.
This makes it very quick and easy to recognise the right time to air out the room, namely when the light is yellow or red.
Additionally, there’s a Bluetooth Low Energy (BLE) module built into the Sensirion’s circuit board. It transfers measurement data every few seconds from the sensor to the My Ambience smartphone app. In the app (available for Android and iOS), you can then view the development of the CO₂ concentration as a line graph.
The lowdown: a sensor with many possibilities
The CO₂ sensor is practical; the LED indicates how good the air quality is in a simple and understandable way. In an office or classroom, all you’d need to do is plug it into a laptop for everyone to see the air quality. In addition, you can view measurements over longer periods of time and read out data in the app. The only drawback: USB-A is increasingly being replaced by USB-C; as a result, the Sensirion sensor no longer fits in new MacBooks, for example.
Aranet 4 Home: the independent long-distancer
With a price of over 150 francs or euros, the Aranet 4 is a rather expensive sensor, but it can do quite a bit in return. Above all, it impresses with its quasi-infinite runtime. Equipped with two LR6/AA batteries, the sensor, manufactured by a Latvian company, lasts months at a time.
The square case measures only 7×7 centimetres. At the back, there’s a recess that allows you to hang the sensor using a nail, for example. Then again, the Aranet’s modest aesthetics rather speak for a not-quite-so-prominent placement. The semi-transparent plastic lets the circuit board show through. In addition to its sensors, the Aranet 4 also contains a Bluetooth module, used to connect to the app (available for iOS and Android).
In the app, you can view progress charts – also for air pressure. In the app, you can also set how often the display updates. With an interval of five or ten minutes, the Aranet will run not only for months, but two to three years on a single pair of batteries. I can also set the app to vibrate if the CO₂ concentration exceeds 1,400 ppm – convenient.
Even though the app is comprehensive and provides a lot of data, Aranet also offers a cloud solution for professional use. This is useful when you need to monitor multiple rooms with multiple sensors. In addition to the Aranet 4, you’ll then need a hub, cloud account and subscription. For private use, this is likely overkill.
Conclusion: happily wireless
I almost always take the Aranet 4 Home with me when I’m out and about. On the train, I place it on the little table next to the seats. In a crowded aeroplane, it showed me frighteningly high values even before takeoff. Even without the app, the Aranet 4 offers a wealth of information without having to worry about the power supply.
Technoline WL 1030: inexpensive and app-free
The WL 1030 looks like a weather station. The black, plastic device stands at almost 14 centimetres and needs a constant power supply. It comes with its own plug; no USB cable will help you here.
The fact that Technoline doesn’t have an app speaks for a different target group. The display is the selling point of the WL 1030. It shows the current CO₂ content in the form of a speedometer. Below it is an additional field that indicates the air quality and advises you to air out the room – for example, if the air quality is «medium». It also displays the temperature, accurate to one tenth of a degree, as well as humidity.
The lowdown: for the technologically undemanding
The WL 1030 is for people who like to look at as much weather data as possible without having a smartphone at hand to call up an app. The Technoline WL 1030 is the kind of device you place in a given spot – and leave it there for a very long time. You don’t have much of a choice, as its mobility is very limited due to the power supply.
Accurate enough to be reminded to air out the room
No matter which CO₂ meter you choose, each one will remind you when it’s time to let in some fresh air. Doing so causes the viral load to drop. And the lower CO₂ concentration helps your focus.
Opening windows can be a touchy topic, especially in open-plan offices. A measuring device can take on the role of a neutral watchdog: is the light on or the device beeping? Then it’s time to open the windows for a few minutes until the value has moved out of the yellow or red range. It’s less useful on a plane or train, where it might be better not to know just how bad the air is.
Header image: Martin Jungfer
Martin Jungfer
Head of Content
Martin.Jungfer@digitecgalaxus.chJournalist since 1997. Stopovers in Franconia (or the Franken region), Lake Constance, Obwalden, Nidwalden and Zurich. Father since 2014. Expert in editorial organisation and motivation. Focus on sustainability, home office tools, beautiful things for the home, creative toys and sports equipment.
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