According to the American EPA guidelines, there are minimum efficiency standards in place at 4 counts/hour per pCi/L for active devices. According to the ANSI (American National Standards Institute) and their AARST paper Specifications for Instrumentation Systems Designed to Measure Radon Gas in Air (N42.51):

For the purpose of this standard, a CRM must have [...] a detection efficiency (calibration factor) of at least 2 cph per pCi/L.

However, when discussing the qualities of our Corentium Pro, we prefer to use metrics such as the measurement uncertainty and the standard deviation rather than the simple counts per hour (for more information on what the standard deviation is, you can have a look at this article on our Support Page, referring to our Corentium Home) as they are more reliable and meaningful metric from a technical standpoint.

Other metrics, like the counts per hour, are not an efficient way of calculating how powerful a machine is, let alone the fact that different instruments may even use a different technology on their radon sensors.

In order to avoid the risk of comparing different technologies and detection methods, we rely on the more factual data on measurement uncertainty.

Corentium Pro - Measurement uncertainty: