Security & Saftey

PIR Sensor based Security Alarm System

I will guide you through the process of constructing and setting up a security alarm system based on a PIR sensor in this straightforward do-it-yourself (DIY) project. The core of this circuit utilizes an Arduino as the primary controller, along with the essential PIR sensor. Additionally, I incorporated the UM3561 IC, which serves as a siren generator IC, to produce the necessary alarm sound through a speaker.

PIR Sensor based Security Alarm


  • Introduction
  • PIR Sensor based Security Alarm Circuit Principle
  • PIR Sensor based Security Alarm Circuit Diagram
  • Circuit Components
  • PIR Sensor based Security Alarm Circuit Design
  • Code
  • Working of PIR Sensor based Security Alarm System
  • PIR Sensor Based Security Alarm System Applications
  • Limitations of this Circuit


Typically, security systems in homes, stores, offices, and various other settings rely on infrared or laser transmitters and receivers for accurate and reliable operation. However, implementing these solutions can be quite costly and often requires substantial infrastructure support.

This project offers an alternative, cost-effective approach to security systems. I will introduce a PIR-based Security Alarm System, which utilizes a PIR sensor in place of traditional transmitters or receivers. This approach not only reduces power consumption but also presents a budget-friendly solution. PIR stands for Passive Infrared Sensor, and it forms the core of this system.

PIR Sensor based Security Alarm Circuit Principle

The primary objective of this circuit is to enhance security. It achieves this by incorporating a PIR sensor and an IC for siren generation. The PIR sensor is responsible for detecting infrared (IR) radiation emitted by individuals, resulting in a digital output signal. This digital output is received by the Arduino UNO microcontroller.

Subsequently, the Arduino UNO utilizes the received data signal from the PIR Sensor to activate the UM 3561 siren IC. Whenever a human presence is detected, the siren emits sound.

The UM3561 is an integrated circuit with a built-in read-only memory (ROM). It is capable of generating various siren sounds, including those resembling ambulance, fire engine, police, and machine gun sirens.

PIR Sensor based Security Alarm Circuit Diagram

Circuit Components

  • PIR sensor
  • Arduino UNO
  • UM3561 Siren IC
  • NPN Transistor – 2N2222
  • Resistors 10KΩ and 220KΩ
  • Speaker 8Ω
  • Breadboard
  • Connecting Wires

PIR Sensor based Security Alarm Circuit Design

The designed system consists of several components, including the Arduino UNO, PIR sensor, UM3561 IC, speaker, transistor, and several resistors. The UM3516 serves as the Siren generator IC and has a total of eight pins. The first and sixth pins are used for sound effect selection, allowing you to choose from four different types of sounds depending on their connections.

For my Police Siren project, I left both Pin 1 and Pin 6 open. An NPN Transistor, controlled by Arduino UNO’s Pin 4, connects Pin 5 to +5V.

One end of the 220K resistor is connected to the seventh pin of the UM 3561 IC, while the other end is linked to the eighth pin of the IC. The third pin of the IC serves as the output, which is connected to a speaker through a resistor and transistor.

The transistor’s base is connected to the IC’s output via a 10K resistor. The emitter pin is connected to ground, with one end of the speaker attached to the collector and the other end to +5V.

The output of the PIR Sensor is connected to Pin 3 of the Arduino.


  int pir = 3;
  int siren =4;
  void setup()
  void loop()

Working of PIR Sensor based Security Alarm System

  1. Connect the wires as shown in the circuit diagram and turn the power on.
  2. The PIR sensor is turned on and detects infrared rays emitted by humans.
  3. The range of this PIR sensor is 5 metres. This distance can be varied by adjusting the pot provided for the sensor.
  4. When a human is identified, the PIR sensor outputs a logic HIGH value to ARduino UNO’s Pin 3, i.e. a voltage of 3.5V to 5V.
  5. When the Arduino detects logic HIGH on Pin 3, it sets Pin 4 to HIGH for ten seconds. During this moment, the Siren IC UM3561 is turned on by providing +5V to Pin 5.
  6. Internally, the siren generator has an oscillator that produces the sound.
  7. A 220K resistor is used externally to adjust the oscillator circuit to a specific frequency.
  8. After that, it’s sent to the control circuit, which is controlled by tone selection pins.
  9. These tone selection pins select one tone from the IC’s several tones.
  10. As a result, oscillations and a chosen tone are communicated to the address counter. The data is subsequently sent to the ROM by the address counter.
  11. The tone is then sent to the output pin 3 via the ROM.
  12. The output of the NPN transistor is used to magnify the siren.
  13. The transistor’s base receives voltage from the siren generator’s output pin.
  14. When the transistor receives the cutoff voltage at the base, it begins to conduct, and the speaker is linked to the ground through the negative pin.
  15. When a hum an is recognised, the sound emitted by the speaker can be heard.
  16. It makes a Police Siren sound in the current circuit.

PIR Sensor Based Security Alarm System Applications

  • This can be used to secure important items in museums.
  • This can also be utilised as a doorbell circuit that automatically sounds the bell when a human is identified.
  • This could be utilised in defence applications to detect humans in the field of battle.
  • This can be utilised in sound-producing toy applications.

Limitations of this Circuit

  • PIR sensor pot should be adjusted in such a way to detect the humans only.
  • This can detect the human only within its range of 5 meters.

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