【正文】 ed the system security, and greatly reduced the cost.Keyword: Monolithic integrated circuit, Automobile security system , Code/decodeIntroductionIs unceasingly progressive along with the social economy and the high tech rapid development, in the routine work and the life, the automobile has bee the people ideal transportation vehicle. But the following motor vehicle the case which robbed gradually is also in creased has created the pilot economical property loss. In order tore duce the automobile to rob the event the formation rate, for has the automobile the user to provide the safety control, simply develops one kind to be reliable, the ease of operation, can send out in the discovery normal condition to the pilot reports to the police the reminder and the security warning safety system has the practical significance. This article based on to the existing automobile security alarm system generalized analysis, develops one kind of brandnew security alarm system. This system has mainly used the jump code code/decoding principle, causes the overall system to be safer, greatly reduces password explaining rate.1. System principle of workThe automobile security alarm system the remote control which carries by the driver and installs in the automobile the controller two parts poses. The remote control and the controller all use eight CMOS which American ATMEL Corporation produces the AVR monolithic integrated circuit, this series monolithic integrated circuit based on new simplifies instruction R the ISC structure, includes the service life most to be few is 1,000 time writes/scratches the circulation the Flash program memory, as well as the service life at least is 100,000time writes/scratches the circulation E the EPROM datacarrier storage, some 2 only have when the entire piece cleaning can clean the programming encryption locks the localization. System designThe automobile security examination uses the ultrasonic sensor. The ultrasonic sensor is posed by the ultrasonic wave transmission circuit and the supersonic reception electric circuit, in the automobile cab appropriate position, installs the ultrasonic wave launch/receiver, as well as switch electric circuit T1. When the automobile parks the vehicle owner person must leave the automobile, with remote control closed switch T1, the automobile alarm system sat garrisons the condition, around the system use ultrasonic wave examination vehicle obstacle. Launches the partial electric circuits likes chart 1 to show. When its P1 mouth , to the D trig , the control ultrasonic wave launch, are 0, the photo electricity coupler outputs the TP1 end is 1, the permission ultrasonic wave launch, launches/the receive ultrasonic wave in turn, the circulation repeatedly carries on. Simultaneously the monolithic integrated circuit interior counter starts to count. The steam distance between vehicles ob