Because the air pressure inside a house is typically lower than the pressure in the soil around its foundation, radon is drawn into the home through cracks in the foundation and other openings. Radon levels are measured in picocuries per liter, or pCi/L. Levels of 4 pCi/L or higher are considered hazardous.
Short-term radon tests take between two for residential and individual self-testing to 90 days to collect readings from your home, depending on the manufacturer. You must then send these test kits to a laboratory to have the results calculated and returned to you.