Air pollution poses a great environmental risk to health, accounting for nearly half a million premature deaths each year in Europe. Biogas production is an enabling technology to achieve net-zero emissions, while accelerating the energy diversification in Europe. Both, air quality control and biogas production demand critical improvements in sensor technology. SYMPHONY will develop a new technology enabling the implementation of dense networks of cloud-connected, low-cost, portable and easy-to-use sensors, capable of multi-target detection for applications in air quality control, pollution monitoring, industrial process control and safety. SYMPHONY will address this challenge by making key developments in silicon photonics, neuromorphic circuits, artificial intelligence, integration, and packaging, while exploiting state-of-the-art silicon microelectronics for ultra-low power edge computing with artificial intelligence, and the connected sensor network for spatially-resolved analysis and prediction. The main focus of SYMPHONY smart sensors are gases related to the biogas production and gases that have been identified by the European Environmental Agency (EEA) as highly pollutant and contributing to the greenhouse effect, such as CO2, CH4 and NO2. SYMPHONY smart sensors will be validated in three different relevant scenarios: city pollution monitoring in Cyprus, process control and leakage detection in biogas micro-plants in multiple locations in Europe. With this ambition in mind, SYMPHONY has gathered a transversal consortium, comprising three academic institutions, two research institutes, four companies and two end-users, coming from seven different countries in Europe. The consortium covers the full value chain, including silicon photonics, neuromorphic circuits, silicon microelectronics, integration, packaging, artificial intelligence, gas sensing, the internet of things, biogas production and air pollution monitoring.