The Pro is meant to be used indoors during home inspections in rooms where occupants would spend most of their time.
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If you used your device in humid environments and are getting error messages, remove the Pro and set the device in a dry environment for 24 hours before trying a reset.

When doing an official radon measurement, remember to stay within the Operation environment:

5% Relative Humidity to 80% RH non-condensing

39°F to 104°F / 4°C to 40°C