Inductive anti-theft alarm circuit using field effect tube

Inductive anti-theft alarms use human body induction to alarm when the human body is a certain distance away from the induction piece. The circuit of an inductive anti-theft alarm
    using a field effect tube is shown in Figure 13-159. The monostable circuit is composed of 555 time base integrated circuit A and so on .     Adjust potentiometer RP. The sensitivity of the device can be changed. The sensitivity should be as high as possible, but not too high to avoid false alarms.     The alarm delay time is t-1. lR2 Cz, so the values ​​of Rz and C2 can be adjusted to change it. According to the component parameters shown in the figure, the alarm delay time is about 40s.