I'm pulling frequent measurements of household radon levels into Home Assistant, using an integration with my Airthings radon sensor. The levels are much lower than they used to be, a day after we turned on a new radon mitigation system. This is the "yay we did it" point of a project that has been nagging at me for a long time.
If you live in a house in an area with elevated radon levels, I would encourage you to skip the multiple years it took me to get everything sorted out. Here's what I would tell my earlier self.
There's two ways to test for radon. One is a one-time kit, that you set into a room and then send back to a lab for results. They are cheap (or maybe free from your health department), but they give a one-time reading. The other is with a sub-$200 electronic sensor that does a continuous readout, measuring every few minutes and reporting to your smart phone and a cloud server. I totally and completely recommend spending less than $200 to get something in place to monitor over time and to help you be sure that any mitigation you put into place actually works.
The Ann Arbor District Library has radon measurement tools for checkout. You can also buy them for continuous monitoring. Mine is from Airthings.
https://aadl.org/catalog/record/10625120
When you run the sensor for a while, you will discover that levels vary depending on the time of day, atmospheric pressure, the phase of the moon (?), and other things that seem to be random. You will also note that if you have a room that doesn't get much ventilation that the levels will build up. We have a whole-house fan connected to our thermostat, and running more frequently kept the levels down some. Cracking open a window to let in fresh air will also help. We saw a variation around a mean with a 50% +/- swing either way, and one alarming day that it spiked up to 5x typical readings.
If your radon levels are within a good range (under 50 Bq/m^3 or 1.3 picocuries per liter) you're in good shape. If they are in a bad way you'll want to contact a professional for radon mitigation. (I am not that professional, just a homeowner.)
We got a service to come out and do the work. Day one was about two hours of a two-person job, one inside drilling a hole in the foundation to insert a vent pipe that evacuates gases from under the basement, the other an outside job anchoring that vent pipe and an inline fan to the side of the house where the exhaust gases go above the roofline. Day two was an electrician wiring up the fan and installing an outdoor switch to turn it off in case of maintenance. Your process might be different if you have a different house than ours - in particular there's other things you need to do if you have a crawl space.
Flip the switch, turn everything on, start to monitor the Airthings display on my phone. The levels immediately start to go down and keep going down for at least 24 hours. The new readout (30 Bq/m^3) is in the good range, and the lowest I've seen it since I started watching.
I'm also running Home Assistant which has a very nice set of tools for collecting a time series of data and graphing it. The Home Assistant integration was easy to do (you set up an API key, you plug in the values into HA, and you're good to go).
https://www.home-assistant.io/integrations/airthings/
I'm not generally a big fan of "home automation" as it's practiced, but sure enough sometimes it can be very handy. It would be possible, for instance, for me to have Home Assistant do something really annoying like sound an air horn powered by a smart switch every time the readings went above a threshold.
My rule for home automation is "don't build a haunted house". It's also "keep your family safe from danger". I'm glad I did this project! But I really wish I had someone walk me through it and spell out some options and explain to me just how relieved I would feel now that the Bad Air number has gone way down.
Vendors, for reference; specific contractors for radon work depends on your local area.
Airthings: https://www.airthings.com
Airthings Wave Radon. https://amzn.to/3R3Hpmg This is an Amazon Affiliates link. I would get some small cut of the purchase price if you buy this. I didn't buy mine from Amazon - instead got it direct from Airthings. Your choice.
Protect Environmental Ann Arbor.
These folks did our house. It's the organization formerly known as Protech, apparently some transition to a new name. If you are not in Ann Arbor this company also does business in other locations. My experience was good so far.
Michigan Indoor Radon Program
https://www.michigan.gov/egle/about/organization/materials-management/indoor-radon
From the State of Michigan EGLE, with a map of test results showing typical levels throughout the state that you can zoom into by zip code. Ann Arbor 48104 averages a reading of 4 with a median of 3, within the "Mitigation Recommended" zone.
"Radon", US EPA
National program with maps of areas with high radon concentrations, and links to state and tribal programs for mitigation.
