The possibility of building wireless measurement systems has opened a very intense activity in the field of environmental control and risks. Our daily environment consists of many toxic components, including carbon monoxide (CO), which can be the cause of fatal poisoning. A real need exists to develop sensors that can easily detect and accurately track small concentrations of CO in the air. Another key application of CO sensors is the development of online monitoring and diagnostics systems for reliable and durable fuel cell system operations, since their efficiency is very sensitive to even small traces of CO. The consortium presented in this research project proposes to build a complete CO detection system based on a known precision microbalance quality associated with a specific organic functionalization (e.g. cobalt corroles). Strong complementarities between teams in terms of research and development (associated with high-level academic laboratories) and the possibility to transfer the complete technology for volume production (associated with one industrial) is an essential asset of this project. The current CO sensors are limited either by a low selectivity towards other gases or by a low sensibility, and no rational methodology or integrated approach to fine tune a sensing device for the particular application of CO detection has been developed so far. Our approach is clearly different from the known CO sensor technologies since we propose the use of molecular complexes or functionalized porous materials with specific reactivity towards CO to enhance the sensitivity and selectivity of the sensing layer. The objective of CO3SENS is to address this challenge.