BEHOLDER revolutionises urban security through an integrated and cost efficient platform for real-time detection, assessment, and response to CBRN-E threats. The project addresses the challenges posed by the lack of standards and integration capabilities in current CBRN-E detection systems. Its innovative approach combines IoT-enabled sensors, advanced AI anomaly detection, and seamless integration with smart city infrastructure. The key objectives include the detection of CBRN-E threats in public spaces through IoTisation, the improvement of vulnerability assessments for law enforcement, the enhancement of modelling capabilities for resource planning, and the fostering of market uptake through stakeholder engagement. BEHOLDER utilises cutting-edge technologies such as SmartFurniture, environmental sensor networks, and specialised detectors like IMS+FP, HoloZcan-IoT, RadNano, and BME688 sensors. The project's methodology emphasises a collaborative and capability-driven agile approach, involving stakeholders from the outset. Real-world pilots in urban environments will demonstrate the system's effectiveness, paving the way for wider adoption. By addressing the evolving threat landscape and enhancing urban security, BEHOLDER aims to create safer, more resilient, and better-prepared environments for all. This translates to substantial economic savings, potentially preventing millions of euros in losses from disruptions to critical infrastructure and public services. In a simulated chemical attack scenario in Eindhoven, BEHOLDER could save an estimated €259 million by reducing fatalities, injuries, and healthcare costs. Moreover, the project’s proactive approach fosters a sense of security among citizens, promoting greater public confidence and resilience. By enhancing preparedness and response capabilities, it contributes to safer, more resilient, and economically vibrant urban environments across Europe.