PIR Sensor Working Principle

PIR Sensor Working Principle


Are you curious about how motion sensors work?

If the answer is Yes! then check out this blog post which talks everything about PIR sensors like the workings of a PIR sensor, and exploring its working principle and range of detection.

We also cover how to connect it with an Arduino and what exactly a PIR sensor detects. Join us as we explore the fascinating world of PIR sensors!


The PIR or Passive InfraRed sensor is one of the most used motion detectors.

It detects infrared radiation generated by objects or live animals inside its range of vision, which varies in temperature from warm to cold.

This change is recognized when an item travels across this field, triggering the sensor's alert.

The fundamental operation is to measure the temperature differences between two spots on a passive IR element and then trigger an output signal based on these readings.

Generally, once triggered, PIRs will send out pulses for up to several minutes until no more movement has been sensed in their view area before resetting back into standby mode again where they wait quietly for further activity signals.

With its ease of use and long-range coverage capabilities as well as relatively low cost make it an ideal choice in applications such as home security systems commercial intrusion prevention solutions retail store anti-shoplifting initiatives automated lighting control etc.

PIR Sensor Working

PIR sensors are used in a wide variety of applications such as lighting control, smart home, and IoT applications, Automatic door opening system, Security alarms, and Human detection robots in search and rescue operations in disasters, multifunction printers, etc.

So let's understand what is a PIR sensor and how it works so we can use it in our projects.

What is a PIR Sensor?

A passive infrared sensor is a small low-priced Passive infrared motion detector sensor.

As the name suggests it doesn’t emit radiation (unlike an Infrared (IR) sensor which emits infrared radiation) but it detects the changes in infrared radiation of the source. It's very facile to use and hence used in diverse applications.


PIR sensor

PIR Sensor Working Principle

It works on the principle that whenever it detects a change in infrared radiation, it generates a digital output signal.

PIR Sensor Working Principle


PIR sensor consists of a fresnel lens, pyroelectric material (metal can and a rectangular crystal).

A Fresnel lens which is made of high-density polythene concentrates the incoming infrared radiations so that they fall on the pyroelectric material.

Metal can help to make the sensor more immune to temperature, humidity, and noise. Pyroelectric material detects the changes in infrared radiation and generates an output signal.



It is made up of 2 slots of special material sensitive to IR. When a person comes in the range of the sensor, the first slot creates a positive differential voltage and when the person leaves the second slot creates a negative differential voltage. These changes are detected.


This output signal is further processed by the external circuitry and converted to digital output.

Read our blog explaining the IR sensor working where we explained the types of IR Sensors, how an IR sensor works with example, and applications of IR Sensors.

What does a PIR sensor detect?

Passive infrared sensors can detect human or animal motion. Humans emit infrared radiation.

When a human comes into the sensing range of the sensor, these changes in radiation are detected by the sensor which causes the output of the sensor to go high.

What does a PIR sensor detect

PIR Sensor Range

Passive infrared sensors are available in a wide range of options:

Indoor curtain-type PIR sensor: Range is between 25 cm to 20 m

Indoor passive infrared: The range is between 25 cm to 20 m

Outdoor passive infrared: The range is between 10 m to 150 m,

Outdoor passive infrared curtain detector: Range is between 10 m to 150 m.

Considerations For Installing a PIR:

Here are some key considerations while installing a PIR (Passive Infrared) sensor easily and effectively:

Installing a PIR
  1. Know your sensor's range and detecting capabilities. This allows you to determine where to position it for the greatest results.
  2. Locate a position on the ceiling or wall that provides a clear view of the area you wish to monitor. You may place it near the lights to automate them.
  3. Install the sensor using screws and adjustable brackets. Position it to watch the entrances and hallways.
  4. Avoid hot places and sunshine. They issue terrible notifications. Move the sensor away from heaters, air vents, and direct sunlight.
  5. Position the sensor 2-3 meters (6.5-10 feet) above ground. This height is optimal for properly covering the region.

How to connect the PIR sensor with Arduino?

PIR Sensor has 3 pins: VCC or 5V, Gnd, and a digital output pin. This digital pin is used to communicate with the microcontroller.

Connection diagram


How to connect the PIR sensor with Arduino


As shown in the image, Vcc goes to 5V, Gnd goes to Gnd, and Output is connected to digital input pin 2 of Arduino. 

Whenever there is motion detected output pin of the PIR motion sensor goes high.

So based on this result we can read the digital input pin 2 of the Arduino and take the action such as glowing LED.



You can put the Passive infrared sensor in two modes as shown in the above image the jumper is used to connect it in H mode repeatable trigger and L mode non-repeatable trigger.

In retriggering or H mode, the LED stays on while the person is moving in the PIR sensor range. Whereas in non-retriggering or L mode, LED blinks or turns on and off every 1 second when a person is moving in the PIR range.

Also, there are two potentiometers of 1M ohm resistance available for adjusting sensitivity and time delay as shown in the image. 

The sensitivity pot is used to adjust the distance from 2-5m and the time delay pot is used to adjust the

time for which the output pin should remain high when the motion is detected.

You can set the range from 5 seconds to 5 minutes. Turn it fully anti-clock so

that you can decide the time delay from Arduino.

Below is the Arduino code to detect motion using the PIR sensor:

Arduino code for PIR Sensor

 int led = 13;    // led is connected to pin 13

int sensor = 2;  // output pin of the sensor is connected to digital pin 2

int val = 0;     // variable to store the sensor status (value)

void setup()


    pinMode(led, OUTPUT);   // initialise LED as an output

    pinMode(sensor, INPUT); // initialise sensor as an input

    Serial.begin(9600);     // initialise serial


void loop()


    val = digitalRead(sensor); // read sensor value

    if (val == HIGH)

    {                            // check if the sensor is HIGH

        digitalWrite(led, HIGH); // turn LED ON

        delay(1000);             // delay 1000 milliseconds

        Serial.println("Motion detected!");




        digitalWrite(led, LOW); // if val is low , led pin set to low

        delay(1000);            // delay for 1000 second

        Serial.println("Motion stopped!");



Also, read our blog Types of Proximity Sensor detailing 5 types of proximity sensors and their working principles.


In this blog article, we learnt that the passive infrared sensor is a very adaptable and dependable technology that is ideal for motion detection applications.

Its simple working concept and intuitive interface enable it to detect motion and presence with high accuracy. An effective instrument for seeing intruders, turning on lights, and sounding alarms is a passive infrared sensor.

You can quickly connect a passive infrared sensor, or PIR, to an Arduino and begin detecting motion right away by following the steps in this article.

So why are you hesitating? Get a PIR sensor now to enjoy the advantages of motion detection for yourself!


If you appreciate our work don't forget to share this post and leave your opinion in the comment box.


Please do check out other blog posts about Types of Sensors in IoT , Interfacing Proximity Sensors with Arduino and How DHT11 and DHT22 Sensors Work and interfacing it with a MCU on Proteus


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Frequently Asked Questions

1. What does an PIR sensor do?

The PIR sensor is a device that detects motion by measuring the infrared radiation emanating from the object. It employs a pyroelectric sensor that transforms the infrared radiation into voltage, which is then processed to identify the movement. Once the object enters its radius, it recognizes the alteration in infrared radiation and emits an output signal, which triggers various devices such as alarms, lights, and occupancy sensors. These sensors are highly utilized in the security, lighting, and occupancy sensing industries.

2. Does PIR sensor work in sunlight?

PIR (Passive Infrared) sensors detect changes in heat emitted by objects within their range and are not affected by visible light. However, direct sunlight hitting the sensor may cause it to generate false readings since sunlight emits heat and can trigger the sensor. Therefore, PIR sensors should be shielded or placed in a location where they are not exposed to direct sunlight in order to function correctly.

3. Does PIR work in the dark?

Passive Infrared (PIR) sensors detect infrared radiation emitted by warm bodies and can operate in complete darkness. PIR sensors do not rely on visible light to detect motion or heat signatures, making them an effective solution for detecting intruders or movement in low-light or dark environments. PIR sensors are commonly used in security systems, lighting controls, and other applications where motion detection is necessary in the absence of visible light.

4. What is PIR sensor full form?

Passive Infrared detection is a common technique in security systems. It detects movement or intruders by recognizing the infrared light produced by the nearest objects. 

5. What is the difference between PIR and IR sensors?

The main difference between PIR (Passive Infra-Red) sensors and IR (Infrared) sensors lies in how they operate. IR sensors emit infrared radiation to detect the heat or movement of objects, measuring only the infrared radiation emitted by those objects. Conversely, PIR sensors detect infrared light radiating from objects within their field of view. PIR sensors don't emit infrared radiation, rather, they passively detect infrared light generated by objects.

6. What is the range of PIR sensor?

The range of a PIR sensor changes with its type and application. Indoor detection distances for ordinary and curtain-type sensors generally range from 25 centimeters to 20 meters. Outdoor PIR sensors, built for external monitoring, with detection lengths ranging from 10 to 150 meters. 

7. What can PIR detect?

Security systems commonly use PIR detection to identify movement or intruders. It works by detecting infrared light emitted by nearby objects. PIR sensors basically identify changes in infrared radiation inside their range of view, which are typically caused by passing humans or animals.

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