This burglar alarm system circuit is using a infrared proximity detector that triggers an alarm when the rays falling on its sensor are interrupted. It is different from others burglar alarm systems because is a very simple diy project and can offer you great satisfaction.
The circuit of IR burglar alarm system comprises transmitter and receiver-cum-alarm sections. It works off 6V DC, 500mA uninterrupted supply and uses low-cost readily-available electronic components. LED2 is used for indicating power-on. Check out the infrared alarm circuit too.
Burglar alarm circuit diagram
The transmitted IR signal directly falls on IR sensor TSOP1738. Whenever the IR signal is interrupted, its output pin 3 goes low and IC2 is triggered at pin 5 through transistor T2. As a result, its output at pin 7 goes low (for a preset time) to forward bias siren-driver transistor T2. This condition is indicated by the glowing of LED1. The time-out period can be increased or decreased by changing the value of capacitor C6.
The output tone of siren-sound generator IC3 can be set by connecting its pin 6 to either Vcc or GND.
When you connect pin 6 to Vcc IC3 produces the sound of fire-alarm siren, but when you connect it to GND it produces the sound of ambulance siren.
Burglar alarm assembly
Assemble the transmitter and receiver-cum-alarm circuits on two separate general-purpose PCBs and house in suitable cabinets. Mount the units on the opposite sides of the entrance gate such that IR rays from IR LED1 fall directly on the IR receiver module.