Radon levels will change when you open a window especially if the window is in the same area as the test kit. In general however the window or multiple windows have to be wide open in the test area to make a big change (cut radon levels in half). Opening windows can bring marginal radon levels below the guideline. Opening windows on floors above the area being tested can cause the radon levels to go either higher or lower. Moving the radon detector to a low radon area will obviously also change the results to the new location level but many testers will minimize this possibility with tamper resistant features. We have a full report on test tampering available as a download. Whether you believe radon is over-hyped or not, the EPA risk table graphically illustrates that the exposure risk is very serious and lung cancer is the most deadly cancer.