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Radon: how is radon measured? How does an Airthings device measure radon?
Radon: how is radon measured? How does an Airthings device measure radon?

Applicable to the Home, Wave Radon, Wave Plus, View Plus and View Radon

Updated over a week ago

The Sensor

The radon sensor in all of our products is made by Airthings and uses "alpha spectrometry" to measure the level of radon. It was designed by our in-house CERN scientists and the invention is patented. CERN stands for the European Organization for Nuclear Research.

The radon sensor consists of a passive diffusion chamber, which allows air samples to flow into it. There is a photo diode located inside this chamber, which essentially counts the amount of "daughter" radon particles in the air sample.

“New” air fills the passive diffusion chamber sensor in about 30-45 minutes. The sensor itself (photo diode inside) counts events continuously and it keeps a ledger of these counts on an hourly basis. In order to calculate the actual radon concentration, there is quite a lot of maths involved. A new calculation runs every hour and includes the counts for the past 24 hours, therefore, every hour there is a new update to a 24-hour average.

This same radon sensor is in any of our products that measures radon, i.e. the Home, Wave and Wave Plus. The Corentium Pro (our AARST-NRPP, NRSB & C-NRPP certified device) even has the same sensor, except there are four of the same sensor inside.

How radon is measured

Radon is not an instant measurement, like temperature for example: radon is measured as an average value. In practice, this means that the sensor counts the alpha particles of radon for each sample of air it analyzes. The detector works continuously, then every hour it produces a data point that contributes to an average reading. This is why you can see your radon levels as the averages over 24hrs, 48hrs, a week, month, etc...

All of our homeowner products are designed for domestic use. This means that they are designed, made and sold to collect long term averages. This is an important thing to keep in mind: professional devices are usually equipped so that they can perform a very high number of counts per hour. Our Corentium Pro is a continuous radon monitor that does exactly that - and it is equipped with 4 sensors working in parallel.

For the average consumer use, this is not necessary as long as the device collects enough data points: since the measurement is fundamentally an average of the amount of the radon (Rn222) alpha particles present in all the samples of air collected by the sensor, this means that the longer the measurement, the more data points, the more accurate the readings become. This is an important thing to highlight: we usually recommend you measure for as long as possible, for at least 30 days. After one month, in fact, you have probably gone through a wide-enough range of temperatures, humidity levels, maybe you have experienced a few days of rain, etc. and your detector has gathered enough data to start indicating a pattern: the average will eventually settle on a reference level.

How Airthings devices present your radon levels

Corentium Home

The Corentium Home is a stand alone device which has a display, offering:

  • Short term averages - a 1 day average, 7 day average 

  • Long term average - accumulative of the amount of days you've been measuring (can hold 1 year's worth of data).

    For more detail, please check this out.

Wave Radon, Wave Plus & View Plus

Wave Radon, Wave Plus and View Plus all have the same radon sensor, but connect with an App on your phone, allowing you to visualize your radon data and observe trends in radon behaviour in your environment. You can view your radon levels:

  • In the App - trends, graphs and color indicators 

  • In your online dashboard - offers even more detail, where you can also download and analyze your own raw data.

  • Data is presented as averages over 24hrs, 48hrs, one week, one month, etc...

The averages provided are always "rolling" averages, and radon measurements are updated hourly.

This means the 1 Day average (or 24hr average) you see, is always the average level of radon in the last 24hours. This updates every hour.

In practical terms, this means that if you had an abrupt change of radon concentration from - say - zero to 1000 (and held it there), the expected reading would be a rising concentration level over 24 hours until it reaches the new steady state. This means you won't see a dramatic change in levels immediately if you decide to ventilate heavily for 1 hour alone.

It is important to note: the statistical nature of the detection of the alpha decay adds a random component to the radon count, and the way the app presents the data. This introduces another level of averaging depending on the time window the user is looking at in the plots.


Our sensor has been tested by independent labs around the world, and we obtain a Calibration Certification from the German Federal Office for Radiation Protection on an annual basis. Based on these tests, the accuracy/precision of our sensor is stated as the following:

Accuracy/precision after 30 days of continuous measuring:

  • Typical σ for 7-day average is: ~ ± 10% at 200 Bq/m3 or 5.4 pCi/L

  • Typical σ after two months: ~ ± 5% at 200 Bq/m3 or 5.4 pCi/L

This means that if you measure for 30 days continuously, and then check your "1 week average" figure for the last 7 days, the readings would be ~ ±10% of the actual radon level, if the levels were approx. 200 Bq/m3 or 5.4 pCi/L. At this level, this means the monitor could show:

  • A measurement between 180 Bq/m3 and 220 Bq/m3

  • A measurement between 4.86 pCi/L and 5.94 pCi/L

If you measure for longer, such as 2 months, and then view the average radon level for that 2 month period, the level you see would be ~ ±5% of the actual radon level, if the levels are around 200 Bq/m3 or 5.4 pCi/L.

The reason the accuracy is stated at the particular level of 200 Bq/m3 or 5.4 pCi/L is due to the relation of accuracy and precision. If radon levels are lower, there is more of a chance that the deviation will be greater. If you allow the monitor to measure for longer, it will provide more accurate long term readings, as it gains more data from the air samples obtained.

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