I believe a radon alarm is a necessity in all homes, that have been mitigated. The Radon hasnt gone away, it have been rerouted. For various reasons, this can be interupted - ie contractor comes into home and "borrows circuit" and neglects to reactivate system.
The Alarm is that second line of defense, for the homeowner - all homes have smoke detectors !
I have been contractually requiring them, for all homes mitigated since 2009.
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