This document describes a GSM-based anti-theft system for vehicles. The system uses a microcontroller and GSM modem to send SMS alerts to the vehicle owner's phone if the vehicle alarm is triggered. This provides immediate notification even if the thief gets away with the car, allowing the owner to quickly contact authorities. The system components include a microcontroller, GSM modem, and power supply to integrate wireless features and allow the modem to send SMS messages by serially transferring AT commands.