Perivallon is a European smart infrastructure network that deploys a dense, decentralized network of sensor nodes across urban and rural environments. It provides real-time, hyper-local data on environmental conditions, GNSS anomalies, and aerial activity by fusing signals from space-based systems, atmospheric sensors, and passive RF sources. Designed with dual-use capabilities, Perivallon supports civil and defense applications such as AI-based weather nowcasting, GNSS threat detection, and drone surveillance, all while ensuring sovereign data control and European infrastructure compliance.