The components of the alarm system are fully enclosed within a portable housing and require no external power or data signal connections. A mobile transmitter generates a proximity signal indicating a given range from the vehicle. An audible alarm signal and a GPS location signal are generated in response to the output of one or more sensors indicating a particular occurrence, if a transmitter is outside of the given range, indicating that the driver has left the vehicle unattended and vulnerable to attack. When the vehicle is driven by an authorized driver having the transmitter, the received proximity signal indicates that the driver is within the given range, preventing the generation of the audible alarm resulting from sensors being triggered by shifting cargo in the cargo compartment resulting from vehicle movement and irregular road surface conditions during transit.