In order to solve the problem of the existing anti-theft device easily to be cracked and reproduced when communicating at a fixed-frequency, a new anti-theft device was designed on nRF905 which had the function of frequency modulation. Since the communication frequency was kept changing， the information could not be interfered or intercepted，and the anti-theft device was difficult to be reproduced and cracked．Through the communications program optimization and program design, the reliability of the frequency-hopping communications was improved. The car owner could gain prompt access to car conditions and alarm information through the two-way communication function. The multi-sensor detection circuit design could improve the reliability of the anti-theft device. The new anti-theft device has been tested to have a good effect，so it has good prospects of application.