The second leading cause of lung cancer in the U.S. (smoking is #1) is Radon. Radon is a naturally occurring radioactive gas in the ground. When Radon has accumulated in a structure in sufficient quantities, it may present health risks over time. Homes with basements are particularly at risk. Levels of radon gas that exceed governmental guidelines have been found in Arizona, as well as in every other state. Home radon test kits can be bought for $15 at They have to stay in one place at least 48 hours (best is much longer), can only test that one location (other rooms may have different levels), and need to be sent to a lab. An alternative is a smart detection system costing $200 called the Wave. It warns of elevated levels at a glance, can be moved around the home, and is more accurate than the single use tests according to Consumer Reports.