The main goal of this work is to design an efficient and cheap car-alarm with an electricity consumption not exceeding 1mA in the stand-by mode. The first part focuses on the conception of the car-alarm. As the best option - GPS/GSM car-alarm conception is chosen. Then the design of the switching power supply, communication via RS232 with the GSM module, and GPS module, I2C communication with accelerometer and timer IC, and design of the display module are described. Furthermore, the process of how to code/decode sms into the PDU format is also discussed in this part. The second part provides some basic empirical characteristics of the switching power supply (efficiency, switching frequency etc.). Then the owchart of the main loop is explained, followed by an example of the sms which the car-alarm sends in case a car theft. Explanation of how to set up timer, acceleration threshold and the time between the check of the sms commads is the subject of the next section. Fifth part deals with the installation the car-alarm into a car which is illustrated on the Skoda Favorit example. Total costs and also different cost items are listed just before concluding and suggesting some potential improvements of the device.