Anti-theft alarm circuit

Circuit working principle: This early warning device is essentially an induction sequence switch circuit
to achieve the purpose of correctly connecting the phone and dialing the number. When someone is within 50 cm of sensor
G , human body clutter is received by G, causing the resistance between the drain and source of field effect transistor VT1 to increase
. Pin 2 of IC 1 is low level , and the monostable delay composed of IC 1 When the circuit is working, pin 3 outputs high level and K1 is closed. The contact point of K1 is connected to the hands-free switch of the telephone set.