Radon gas is a leading cause of Lung cancer. Charcoal test kits only give you a small window view to your Radon levels. Radon levels vary over the year and change with the weather. I've only been able to find one inexpensive electronic radon gas detector. Unfortunately it isn't set up to collect data. I wanted to work with the local schools to collect radon and weather data to correlate.
Here is a "hack" to collect radon data: http://www.howmuchsnow.com/arduino/radon/