AX-Guard is a distributed EV fire detection and underbody cooling infrastructure for smart-city, smart-venue and shared parking ecosystems. Each designated EV bay receives a floor-mounted node combining active off-gas sensing, optical temperature sensing, Edge AI cross-validation, local valve control and an underbody sprinkler. Internal validation recorded precursor detection within 3 seconds, actuation within 5 seconds and a false-positive rate below 0.5%. Each node operates locally during network outages while reporting bay-level status to a centralized web dashboard. More than 220 L/min is directed toward the battery pack to slow thermal escalation, while perimeter nozzles form a water curtain that limits propagation. The anchor-bolted, low-profile retrofit design allows municipalities and property operators to protect selected EV bays incrementally without reconstructing the entire parking facility.