A new generation of electronic radon (222Rn) detectors has emerged over the past decade. These are inexpensive devices that use passive 222Rn sampling and are based on ionization chambers or diode detectors to detect the alpha particles emitted by 222Rn and its short-lived progeny. Combined with appropriate data collection and storage protocols, these detectors have proven to be very effective for generatingreliable time-series data of 222Rn concentrations in dwellings and workplaces.