Radon is measurable, my CO2 detector also mesures radon. There is none in my well-insulated house. Now in a basement in Brittany things would be different, but

Radon is measurable, my CO2 detector also mesures radon. There is none in my well-insulated house. Now in a basement in Brittany things would be different, but for most houses in most places, radon is negligible. There also isn't a notable difference in cancers between radon-rich granitic places like Brittany and the rest of France. I feel like at least in France, the potential dangers of radon are well known.