Radon is a naturally-occurring radioactive gas that can cause lung cancer. Radon gas is inert, colorless and odorless. Radon is naturally in the atmosphere in trace amounts. Outdoors, radon disperses rapidly and, generally, is not a health issue. Most radon exposure occurs inside homes, schools and workplaces. The EPA estimates 1 in 15 homes has elevated levels of radon.
When buying or selling a house, it's a good idea (and required in some counties) to have your property testing for the present of radon.
$149 in Baltimore City and Baltimore County.
Other counties vary.