Abstract: A mountable device and system for leakage detection and monitoring of various hazardous materials that can be stored and transported in variety of containers, including ones mounted in railroad cars, tank trailers, trucks, and other dedicated vessels. The device includes a sensor array to detect a potential leakage, wireless communication means, processor and the batteries in a single enclosure. The device can be readily mounted and dismounted using a dedicated opening in container's valves protection box or its lid and provides communications with a respective wireless sensor network.