Abstract: A vehicle security system can be fitted to a vehicle which has a radio transmitting device such as a cellular telephone, PMR or CB set. A control unit is arranged to periodically alert the driver of the vehicle to record a location message. When an alarm condition is signalled to the control unit from an alarm system, a panic button or a ratio receiver co-operable with a remote panic button transmitter, the control unit initiates a transmission from the radio transmitting device. The message transmitted includes the last recorded location message and may also include vehicle identification information and a mileage update message generated in response to the output of a vehicle odometer to indicate the distance travelled by the vehicle since the last location message was recorded by the driver. The same security system may also be constructed as a portable unit.