There are two primary types of radon testing. You can choose to use a short-term test kit, which is usually placed and left for a period of up to 90 days, or a long-term kit, which is designed to measure seasonal fluctuations in radon levels. Long-term kits are left in place for 90+ days.
Most radon test kits consist of a charcoal canister or a similar material, which can pick up and trap small amounts of radon. Using lab tests, the amount of radon in a test kit can be determined, and the overall radon levels in your home can be measured.
While at-home test kits are available and are effective, hiring a professional such as a home inspector will often provide you with better results, as home inspectors can use higher-quality test kits, and place them in areas of your home where elevated radon levels are the most likely to be found.