One way is to have a professional come in who offers a radon testing service. These services may run as high as $300. Another way is to conduct it yourself with a home test kit. These kits can be purchased at most hardware stores for around $10 to $20, which includes the cost of mailing and reading the results. If you purchase a kit, ensure that the kit meets the performance requirements in the US EPA radon gas measurement proficiency program which should be stated on the box.
There are two type of kits that can be purchased. The first is a short-term test kit (2-7 days) and the other is a long-term test kit (3-12 months). If a short-term test is used, you should consider running a second test later and the two tests averaged to obtain a more accurate reading.