Pro Home Radon Measurements-630-335-3009. Real estate radon testing in Illinois requires a minimum 48 hour measurement. This type of testing is known as Short Term Radon Testing. Typically, this test involves the use of a Continuous Radon Monitor. This type of monitor will provide same day results, important in real estate transactions. Another method used for testing of radon is the charcoal cannister. Cannisters must be sent to a lab for results taking additional time and results are biased towards the first 12 hours of the actual test. Not too practical when a real estate transaction is involved.