If you couldn’t do a radon test prior to purchasing a home, there are also long term radon tests that are far more accurate. These will test your air for about three months or more. I bought a radon kit for Little House before purchase, but I did it wrong. I put it on an upside down drawer to make it 4 inches off the ground. The home had no utilities so I couldn’t read the directions in the dark and my memory from reading it in the car was incorrect. It wasn’t supposed to be placed that low to the ground. Also, the home was unoccupied for a year, so radon builds up if a home is closed up with no air escaping. My short term test came up with 2.1 which is okay, but in reality it is probably much lower. So I purchased a long term test off of amazon.com after reading Consumer Reports. I bought this one: http://www.amazon.com/gp/product/B003C5BZYA/ref=oh_o01_s00_i00_details
I have yet to tape it up on my walls, but I will update the results down the road once it gets a long enough read.