Testing is the only method for determining if a home is affected by radon. There are typically no apparent symptoms and it usually will take years of exposure before any problems arise. Higher than recommended radon levels have been discovered in every state with stronger concentrations in the North. See the EPA map of Radon Zones.
Exposure to radon in the home is responsible for an estimated 20,000 lung cancer deaths each year. Radon is a health hazard with a simple solution. Read “A Citizen’s Guide to Radon“.