Buy this: https://smile.amazon.com/gp/product/B003C5BZYA/ https://smile.amazon.com/gp/product/B003C5BZYA/ Follow the instructions to the letter (use the hole,

Buy this: https://smile.amazon.com/gp/product/B003C5BZYA/ https://smile.amazon.com/gp/product/B003C5BZYA/ Follow the instructions to the letter (use the hole, tie a string to it and suspend the test in the middle of the room, in an area away from traffic and away from air currents). I recommend using two, on opposite sides of the room. Then leave it there for a year. Many places have seasonal variation in radon, so while you can do a 3 month test, I recommend a 1 year test.