Abstract: Nowadays, a global trend towards increasing the performance of a building is the reduction in energy consumption. In this respect, for existing residential buildings the most common techniques are the application of a thermal insulation layer to the exterior wall of the building and / or window replacements. Unfortunately, their application without proper education of those involved may have a negative effect on the indoor air quality. The use of a continuous monitoring device can give the owner the ability to understand the impact of his behaviour on indoor air quality and, as such, to adjust his routine in order to maintain the indoor air quality at the desired level. This paper introduces a prototype, called ICA system, for continuous, real-time indoor air quality monitoring. The ICA system presents sensors for monitoring the concentration of radon, CO2, CO, VOCs, as well as meteorological parameters, such as temperature, pressure, and relative humidity. Experiments were performed both in laboratory and in situ conditions for testing and validating the proposed system.