To solve the current problem of frequent accidents of children being mistakenly locked in cars, a car alarm system is designed and developed. Using the STC89C516 microcontroller as the core processor, combined with infrared human body sensors and GSM communication modules, real-time monitoring of the situation inside the car and remote alarm for detecting the danger of children being locked can be achieved. The test results show that the design has high sensitivity, reliable performance, low cost, and easy installation, which has high practical value and practical significance for improving children's ride safety.