Given that radon is the second cause of lung cancer after cigarettes, you would think you would notice high levels of this toxic gas in your home. But radon is odorless and impossible to detect (like the iocaine powder in The Princess Bride). A radon tester is the only definite way to tell if radon is present in your home. Radon leaves no evidence until years later, when it may be too late.
Radon can appear in any home, regardless of foundation type. If you are thinking of selling your home, it is particularly important for you to test for radon and fix the problem before attempting to sell your home; many buyers will want to test for it, and given how quickly a real estate transaction can take place, they may reject your home out of hand when they discover the presence of radon. A radon tester can help you avoid such complications and delays when you are trying to sell your home. Radon can usually be mitigated with a special venting system. You can contact a radon mitigation professional to get a cost estimate.
You can get both short and long-term radon testers. In either case, it's crucial to read and follow the directions carefully. A radon tester should be placed on the lowest lived in-level of your home (your basement if you use it frequently, otherwise, on your first floor.) Generally speaking, they should be placed a foot or two above the floor—check your instructions for exact height.
You can get a map to determine the percentage of homes in your area with high radon levels, but remember that even within the lowest-risk zones on the map, there have still been homes that have high levels of radon. Nothing except for a radon tester can accurately reveal the presence of radon in your home. Either way, it's best to know—either you can fix the problem, or you'll have the peace of mind that comes from knowing that your radon levels won't put you at extra risk of cancer.