Amazon sells radon detectors for $150-$200 that function much like a CO detector. You leave it plugged in all the time and it will monitor both short term and long term trends and alarm if the long term average is over a certain threshold. They are not as accurate as the equipment used by inspectors, but the point is they are a longer duration test. Radon levels can fluctuate widely over time. My basement goes from short term around 2 pci/L and will occasionally jump over 4. From research I’ve done it isn’t uncommon for the levels to fluctuate which is why the experts recommend the long term carbon tests regardless of short term tests.