The components of the alarm system are fully enclosed within a portable housing and require no external power or data signal connections. An audible alarm signal is generated in response to the output to one or more sensors indicating a particular occurrence, if a proximity signal from a mobile transmitter located within a given range of the vehicle is not received, indicating that the driver has left the vehicle unattended and vulnerable to attack. When the vehicle is being driven by an authorized driver having the transmitter, the received proximity signal prevents the generation of the audible alarm resulting from sensor being triggered by vehicle movement during transit including irregular road surface conditions. A GPS unit transmits a signal indicating the state of the alarm and the location of the housing in response to the alarm signal.