Monitoring Radon in the Home via the Adafruit customer support forums.

Radon is a radioactive gas. It comes from the natural breakdown of uranium in soil, rock and water and gets into the air we breathe. Radon can be found all over the U.S. It can get into any type of building and result in a high indoor radon level. It typically moves up through the ground to the air above and into your home through cracks and other holes in the foundation. Your home traps radon inside, where it can build up.

The average indoor radon level is estimated to be about 1.3 pCi/L, and about 0.4 pCi/L of radon is normally found in the outside air. The U.S. Congress has set a long-term goal that indoor radon levels be no more than outdoor levels. While this goal is not yet technologically achievable in all cases, most homes today can be reduced to 2 pCi/L or below.