Radon Mitigation System Installed

If you are looking at buying a home or walking around your neighborhood you may have seen this disk shaped gizmo with a pipe up the side of a house. In the last twenty years there has been a growing interest in testing for Radon (a gas generated deep in the earth as limestone deteriorates) and remediation if it is found at unsafe levels in a home.
Remediation is simple, a small fan is attached to a pipe that is drawing air (and the Radon) from under the homes foundation and expelling it outside.
If you see this you know there is a Radon mitigation system in the home.