You should be able to buy an absorption test kit. For instance in the UK, you can pay £50, you get a couple of detectors to sit in your house for a few months and then you send them to a certified lab.

These kits are fine if you want to check or sell your house - in most cases the amount of radon in your house is determined by your local geology. If you pass an absorption test, it's unlikely you'll suddenly find dangerous levels of radon in the future.

The advantage of the real-time detectors is that they're real-time, but it's hard to prove that they're calibrated.

http://www.ukradon.org/information/measuringradon

I have the AirThings one. I like it. The biggest drawback is that there is no easy way to automatically record readings, so I do it manually.

I move it from room to room every few days. I was surprised that the upstairs bedroom read as high as the basement (but none are high).

Also, as every website points out, the readings vary quite a bit through the day, and from day to day.

I also noticed that the readings increase when it rains (my current theory is that the low pressure that precedes rain pulls more radon from the ground).

Opening windows helps a lot.

I paid a home inspector $150 for a professionally administered radon test so I could be confident in the results. I wouldn't trust something so important to Amazon as they have a lot of counterfeits. Also, if you sell your home you want to show the results to prospective buyers.

Yeah unfortunately they are not cheap; I have two, both by Airthings. I first purchased the Corentium version [shows a 1 day, 7 day and lifetime average], and most recently the "Wave" product [graphs the details over time, also tracks temperature and humidity, transmits results to an app via bluetooth].

I actually went to the effort of decompiling the source code to their Android app as I want to integrate the Wave product to my SmartThings hub so i can automatically ventilate if levels go too high. I find my radon levels build up from around 60 to 200bq/m^3 over time [takes about a month], and my basement walk out opening for 15 minutes once a month tends to lower them < 100bq/m^3 again. The goal i have is to intercept the BT traffic and send it to SmartThings from there over an internet connection or local wifi, ideally automating turning on a vent to the outside that is located near the ground level.

I also learnt a while back that different countries have different levels of "acceptable" radon in residential properties. Currently Canada has a limit set pretty high compared to the rest of the world (200bq/m^3), where as most European countries are suggesting < 100bq/m^3. I found that in the code they consider this when deciding what colour LED to show on the device: https://gist.github.com/ndroo/384bceeb16d771757b6996bd28001d...

The level's they use i personally find a little irresponsible, I'd prefer they pick reliable research (1) and go by that. Experts in Canada acknowledge our recommended levels are out of date and need changing, hopefully an update comes soon that lowers what is acceptable. For now, I've told the app I live in France.

Here is a snippet that I find interesting from the study:

"Radon levels greater than Health Canada’s acceptable limits (of 200 Bq/m3) for the naturally occurring but cancer-causing gas were detected in all areas, with one in eight containing dangerously high radon levels between 200 and an astounding 3,441 Bq/m3. The World Health Organization estimates that the relative lifetime risk of lung cancer increases by 16 per cent for every 100 Bq/m3 of chronic radon exposure. Surprisingly, the scientists found that newer homes, built within the past 25 years, contained substantially higher radon gas levels compared to older homes."

The goal of Airthings states they want "to make radon sensors as common as smoke alarms". I don't know how many lives per year smoke alarms save, i imagine a lot, i would guess if everyone had one of these we would see a massive public health spend drop in relation to lung cancer treatments.

Expensive, but hopefully they get cheaper with time. If you can afford one, get one.

(1) http://cmajopen.ca/content/5/1/E255.full

There are also single-use radon test kits, which should be fine if your home is in a relatively steady-state condition.

The kits cost $13.