48 hour radon test

https://alpha-wiki.win/index.php/Why_Radon_in_Basement_Levels_Matter_Most_for_St._Louis_Homeowners

You place this small device in the lowest livable area of your home, leave it untouched for two full days, then mail it to a lab. The 48 hour radon test measures the average radioactive gas level during that period. It's a straightforward way to see if your family needs ventilation or mitigation work.