A security system and method for monitoring a security status of fixed and mobile assets. The security system comprises an agent connected with the asset. The agent monitors a security of the asset and transmits the data to a master control unit. The master control unit retransmits the security status to a global operations center for processing the security status to detect a security threat. In response to a security threat, the global operations center generates an output. Periodic reports are generated and transmitted to the customer, and the customer is billed at intervals. For mobile assets, the security system also tracks a location of the asset as the asset is transported between a shipper's loading dock and a designated distribution center, including an origination port and a destination port. For fixed agents, the security system includes an interface for interfacing an existing security device to the master control unit and for controlling the existing security system.