The part circuit is as the detection part of the whole system, used to detect theft case, fire, toxic gas leakage and emergency call signals. Theftproof detection is to complete through pyroelectric infrared sensor. Sensors are installed on the balcony, windows and other place where thieves are easy to enter. The part circuit is at the ready state under normal circumstance. Sensors catch theft information when someone enters the scope of the surveillance. Then, wireless module will send the information to the 89C51 single chip computer. The detection of fire and toxic gas is to complete by the corresponding detection sensors, emergency call signal is sent from user hand-hold remote control. B. Wireless Transmitter-receiver Circuit[4] The transmitting and receiving circuit of the part makes use of CMOS manufacturing process produced by a low cost PT2262/PT2272 wireless remote control module. The operating frequency of it is 2 MHz and the communication distance of it is 100 meters above. Under normal circumstances, transmitting and receiving modules are in dormant status. The module is in non-dormant status when be in danger, then coded signal is transmitted. The receiving module has received high-frequency signal decode, generating interrupt signal at the same time. C. Telephone Interface Figure 2 shows telephone interface circuit. The phone lines normal is above 48V DC voltage and optocoupler is not conducting. When the phone lines are ringing signal which is 25±3V sine wave, Optocoupler is conducting, generating interrupted signal to the mainframe. The relay will be connected to J1,after mainframe detected ringing signal many times, then load resistor connected to a telephone line, that computer to simulate the extraction process. Since then, the system access DTMF signals from the TONE of coupled transformer, transmits voice signals from VOICE of coupled transformer. To disconnect the system, the system rings off.