The importance of measuring the decay products of 222Rn (radon) and 220Rn (Thoron) is being realized by researchers as these are the major inhalation dose givers to the general population. Basically the decay products are radioisotopes of Polonium, Bismuth and Lead, which are solid particles. Upon inhalation, these particles deposit in different parts of the respiratory tract, undergo radioactive decay and irradiate the nearby tissues. So, the study of the behavior of the decay products in indoor air is important for assessing the natural background radiation exposures received by general populations through the inhalation route. Although the inhalation doses are predominantly due to decay products yet it had been the usual practice to measure the gas concentration rather than the decay products because of the complexities involved in their detection. The most common method is to derive the progeny concentration from the measured gas concentration using an assumed equilibrium factor. While this is fairly justified for radon in view of the short-lived nature of the progeny as compared to the gas, this approach is beset with serious limitations in thoron-rich environments. However, the development of passive detection system for the decay products known as deposition-based Direct Radon and Thoron Progeny Sensors, has provided a solution to the long standing problem of measuring the time integrated decay product activity concentration. These deposition sensors are calibrated against active measurement techniques, and provide an easy to use method for passive and simultaneous time integrated decay product measurement. In addition, for multi-parametric study, the different modes of these passive sensors, like flow-mode and wire-mesh capped mode, are also used. These are further discussed in the manuscript.