Security systems

A vehicle security system (10) can be fitted to a vehicle which has a radio transmitting device (14) such as a cellular telephone, PMR or CB set. A control unit (12) 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 (22), a panic button (20) or a radio receiver co-operable with a remote panic button transmitter (26), the control unit (12) initiates a transmission from the radio transmitting device (14). 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 (34) 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.