I just wanted to post this out there incase anyone has any ideas how to do this.
Radon detection was brought up briefly in the DIY Kig v3 feedback thread. It seemed to be dismissed as lack of hardware. It appears though that may not be true as i came across this device in on other forums.
Looks to be made by Radon FTLAB though and they have their own Home sensors. Not sure if there is any viability there, but it is a interesting thought.