Low cost and easy to build car anti-theft circuit diagram

This is a car anti-theft circuit diagram to protect and increase the safety of your car to prevent you from being stolen. The circuit is very simple, low cost and easy to build. When the car's key-operated switch S2 is turned on, the 12V DC power supply from the car battery is extended to the entire circuit through the polarity protection diode D5. Flashing LED1 flashes to indicate that the car protection circuit is enabled. It works with the 12V power supply in series with the current limiting resistor R4.

When the door is closed, door switch S1 is in the "on" state, and 12V power is provided on resistor R1. Will this condition happen? Prevent transistor T1 from turning on. In this position, the anti-theft protection circuit is in sleep mode.

When someone opens the car door, switch S1 becomes "off" as shown in Figure #2. As a result, transistor T1 conducts after a short delay introduced by capacitor C1 to trigger relay driver SCR1 (BT169). Electromagnetic relay RL1 is energized and its N/O contact connects power to piezoelectric buzzer PZ1, which begins beeping to indicate that someone is trying to steal your car. To reset the circuit, turn off switch S2 using your car key. This will cut power to the circuit so the buzzer sound will stop.

Collect the circuit on a universal PCB and package it in a small box that fits your car. Connect the switch S1 to the car door and place the piezoelectric buzzer Pz1 at a suitable location in the car.