During the recession a few years ago many home inspectors became FL DOH certified to place and pickup radon tests in the need to supplement lost income.  Some of these inspectors use a passive radon test similar to what we use to test schools and assisted - living facilities.  A passive radon test only provides the client with one number, the average radon level during the test which is normally 48 hours.  A passive test can be carried outdoors during the test or doors and windows can be left open skewing the test results and no one would know. This is a good test (AIR CHEK - radon.com - best),  inexpensive but can be "tampered with" and you wouldn't know. 

Radon is a radioactive gas that has been found in homes all over the United States. It comes from the natural breakdown of uranium in soil, rock and water and gets into the air you breathe. Radon typically moves up through the ground to the air above and into your home through cracks and other holes in the foundation.

Any home can have a radon problem. This means new and old homes, well-sealed and drafty homes, and homes with or without basements. In fact, you and your family are most likely to get your greatest radiation exposure at home. That is where you spend most of your time.

How do I know if there is radon in my home?
You cannot see, feel, smell, or taste radon. Testing your home is the only way to know if you and your family are at risk from radon. The EPA and the Surgeon General recommend testing for radon in all homes. The EPA also recommends testing in schools.
You cannot predict radon levels based on state, local, and neighborhood radon measurements. Do not rely on radon test results taken in other homes in the neighborhood to estimate the radon level in your home. Homes which are next to each other can have different radon levels. Testing is the only way to find out what your home's radon level is.
What can I do to protect myself and my family from radon?

The first step is to test your home for radon, and have it fixed if it is at or above EPA's Action Level of 4 picocuries per liter.
How can radon affect people's health?
Almost all risk from radon comes from breathing air with radon and its decay products. Radon decay products cause lung cancer. The health risk of ingesting radon, in water for example, is dwarfed by the risk of inhaling radon and its decay products. They occur in indoor air or with tobacco smoke. Alpha radiation directly causes damage to sensitive lung tissue. Most of the radiation dose is not actually from radon itself, though, which is mostly exhaled. It comes from radon's chain of short-lived solid decay products that are inhaled and lodge in the airways of the lungs.
What does radon do once it gets into the body?

Most of the radon gas that you inhale is also exhaled. However, some of radon's decay products attach to dusts and aerosols in the air and are then readily deposited in the lungs. Some of these are cleared by the lung's natural defense system, and swallowed or coughed out. Those particles that are retained long enough release radiation damaging surrounding lung tissues. A small amount of radon decay products in the lung are absorbed into the blood.

U.S. Surgeon General Health Advisory

"Indoor radon gas is the second-leading cause of lung cancer in the United States and breathing it over prolonged periods can present a significant health risk to families all over the country. It's important to know that this threat is completely preventable. Radon can be detected with a simple test and fixed through well-established venting techniques." January 2005