Introduction

A Burglar Alarm System is a security device designed to detect unauthorized entry into a protected area and alert the owner by triggering an alarm. It plays an important role in protecting homes, offices, shops, and restricted areas from theft and intrusion.

This project demonstrates how electronic sensors can be used to build a simple yet effective security system.

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Objective of the Project

The main objectives of this project are:

• To detect unauthorized entry or movement.
• To alert users using a buzzer or siren.
• To understand the working of motion or door sensors.
• To design a basic electronic security system.

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Working Principle

The burglar alarm works by detecting movement or door opening.

Method 1: Using IR Sensor / Magnetic Door Sensor

• An IR sensor detects human movement.
• A magnetic reed switch detects door or window opening.
• When intrusion is detected, the sensor sends a signal.
• This signal activates a transistor or relay.
• The alarm (buzzer) turns ON immediately.

Method 2: Using Arduino (Smart Burglar Alarm)

• Arduino continuously monitors sensor signals.
• When intrusion is detected, Arduino activates a buzzer and LED.
• Additional features like delay, password, or notification can be added.

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Components Required

Basic Burglar Alarm Circuit

• IR Sensor or Magnetic Reed Switch
• Transistor (BC547)
• Buzzer / Siren
• Resistors (10kΩ, 220Ω)
• Power Supply (5V–12V)
• Breadboard & wires

Arduino-Based Burglar Alarm

• Arduino Uno
• PIR Motion Sensor or Reed Switch
• Buzzer
• LED
• Jumper wires

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Circuit Diagram

Basic Burglar Alarm Circuit

Sensor Output ---- 10kΩ ---- Base of Transistor (BC547)

Collector ---- Buzzer ---- +Vcc
Emitter ------------------ GND

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Arduino-Based Circuit

PIR Sensor OUT ---- Arduino D2
Buzzer ------------ Arduino D8
LED --------------- Arduino D9
VCC --------------- 5V
GND --------------- GND

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Arduino Code for Burglar Alarm

int pirSensor = 2;
int buzzer = 8;
int led = 9;

void setup() {
  pinMode(pirSensor, INPUT);
  pinMode(buzzer, OUTPUT);
  pinMode(led, OUTPUT);
}

void loop() {
  int motion = digitalRead(pirSensor);

  if (motion == HIGH) {
    digitalWrite(buzzer, HIGH);
    digitalWrite(led, HIGH);
  } else {
    digitalWrite(buzzer, LOW);
    digitalWrite(led, LOW);
  }
}

Code Explanation

• PIR sensor detects motion.
• Arduino checks sensor output continuously.
• When motion is detected, alarm and LED are activated.
• When no motion is present, the alarm remains OFF.

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Advantages

• Simple and reliable security solution
• Low cost and easy to build
• Immediate alert on intrusion
• Expandable with GSM or IoT modules

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Applications

• Home security systems
• Office and shop protection
• Banks and lockers
• Warehouses
• Restricted areas

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Limitations

• False triggering may occur due to pets or environmental changes
• Limited range depending on sensor used

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