Through a practical application, this paper studies the capacity of the GSM network, a wireless mobile phone network widely used in Europe and some Asian countries, for transmitting multimedia data. The application is a client-server based automobile security system which monitors the interior and exterior environments of the moving automobile by a computer equipped a digital camera, a voice capturing microphone and a GPS (Global Positioning Systems) receiver. The captured data is sent to the server computer through the GSM network. The design and construction of the system are described with parameters of the equipment and the procedures of the experiments clearly shown. Results of the experiments show that a basic system can actually be implemented even given the narrow bandwidth of the GSM data transmission system.