The invention describes a tracking, security and status monitoring system (TSS) and modular tracking and security device (MTSD). The tracking and security system includes at least one MTSD adapted for containment within a shipment within a vehicle and for operative communication with a global navigation satellite system (GNSS) (such as the global positioning system (GPS)), cellular networks and a monitoring system. In various embodiments, the MTSD is modular allowing for different sensor systems to be configured to the system, is operative to optimize power consumption and network data usage in the absence of a security event or inquiry from the monitoring system and/or allows the MTSD to recognize when it is within an airborne aircraft to comply with aviation regulations with respect to the operation of RF devices within aircraft. In addition, the system, by using both GNSS and cellular technology (ie. assisted GPS) is effective in being able to determine the real time position of a shipment from a greater number of positions and from deeper within shipment containers or vehicles.