We use test kits from Home Depot. https://www.homedepot.com/p/PRO-LAB-Radon-Gas-Test-Kit-RA100/100141467
And for homes today, at least in areas that have radon (why is easy to find on the web) the builder installs a vent system.
I read this thing on Internet. "Radon is a naturally occurring radioactive gas that comes from the natural breakdown of uranium found in rocks and soil. When radon levels become elevated in your home, apartment or office it becomes a serious health risk. Did you know that radon is the leading cause of lung cancer among non-smokers and the second leading cause of lung cancer among smokers? Testing your home, apartment or office is the only way to know if there is a radon problem. Radon can easily be fixed by one of our certified radon professionals by installing what is called a radon mitigation system or a radon remediation system, also called a radon reduction system."
Now the thing is how to detect this thing with machine or manually i want to know.
Any help will be Thanks.