Instruments for the measurements of radon and its decay products in earthquake research are based mostly on the detection of alpha particles. The devices and methods used, depend on whether the techniques measure radon or radon decay products, and the duration of the measurements, of which there are three types: (i) grab or instantaneous; (ii) integrating; and (iii) continuous. Other criteria used in the design of these instruments are field measurements applicability, portability, convenience and reliability. With the recent increased demand for radon and radon decay products measurements, instruments development has focused on the design of appropriate devices for short-term measurements, as well as on more complex and sophisticated instruments for long-term measurements used in radon research for geophysical, geochemical and hydrological studies.