Abstract: A method and system to continuously monitor the radon concentration in air. As disclosed, these readings are made in situ in a uranium mine to indicate whether safe working conditions exist therein. The apparatus forming this invention has one or a series of detectors each having: a filter network; a flow control valve; a scintillation cell; a flow meter; a gas pump; a photomultiplier tube with a voltage control circuit; and a signal discriminator with an amplifier and shaper circuit. External of the detectors and connected thereto is a counting and recording system which counts and records the voltage pulses which are indicative of the alpha count on the detector cell. When connected seriatim each detector can be sequentially monitored for a predetermined time interval by the counting system so that the local radon level can be continuously monitored for 24 hours per day seven days a week.