I was looking online at detectors in the $150-$200 range, queried a seller's website, asked how the electrons or helium nuclei (aka alpha particles) from radon could be discriminated from other sources. The reply: "Rn222 is the only thing the monitor measures and it is relatively unaffected by anything else. The radon chamber uses passive diffusion and alpha spectrometry to count Rn222 alpha particles - this is achieved through a silicon photo diode. Other particles and rays are discounted through our algorithm." So do the helium nuclei have a specific energy level that can be distinguished from other sources? Is a detector in this price range accurate enough to justify purchase?