Security System Using PIR Sensor


Security system using PIR is an electronic device that allows you to sense motion.  It is used to detect motion whether a human has moved in or out of the sensors range. Motion detector sensors are small, inexpensive, low-power consuming, and easy to use. Due to these features, they are commonly used in gadgets and appliances used in homes or businesses. They are often known as PIR, “Motion detector””Passive Infrared”, “Pyroelectric”, or “IR motion” sensors.

PIR Sensor

PIR sensors basically made of a pyroelectric sensor, that can detect levels of infrared radiation. Everything emits some low-level radiation and hotter something emits more radiation. The sensor in a PIR is actually split into two halves.  These two halves are wired up so that they cancel each other out. One half sees less or more IR radiation than the other, the output will swing low or high.

PIR Sensor Lens

Working of the PIR Sensor

The PIR sensors are more complicated than the other sensors. These sensors consist of Two slots made of a special material that is sensitive to IR. The Fresnel lens are used to see that the two slots of the PIR can see out past some distance. Inactive position, these two slots sense the same amount of IR. The ambient amount radiates from the outdoors, walls or room, etc.

PIR sensor

When any live thing like a human or animal passes by, then it intercepts the first slot of the PIR sensor a positive differential change between the two slots. When a human body or any animal leaves the sensing area, then the sensor generates a negative differential change between the two lost. The IR sensor itself is housed in a hermetically sealed metal to improve humidity/temperature /noise or immunity.

Range of PIR Sensor

  • Indoor passive infrared: Detection distances range from 25 cm to 20 m.
  • Indoor curtain-type: The detection distance ranges from 25 cent meters to 20 meters.
  • Outdoor passive infrared: The detection distance ranges from 10 m to 150 m.
  • Outdoor passive infrared curtain detector: distance from 10 meters to 150 meters


Security System Circuit Using PIR Sensor

We have learned about PIR sensor above, now we study a simple application of the PIR sensor. In the given circuit, we have used the PIR sensor as a motion detection circuit. As anything or human passes IR energy or radiation generated, the infrared sensor detects the energy and immediately converts it into electrical pulses, which is enough to activate the transistor BC547 which activates the relay.

Circuit Diagram of Security system using PIR Sensor

PIR Sensor as switch

PIR As Automatic Door Opening System

This project is opening and closing of doors automatically,  in places wherein the presence of a person is mandatory for example, hotels, shopping malls, theaters, etc. this PIR sensor project is very useful.

Automatic Door Opening System Circuit

  • Security Alarm System based on PIR sensor
  • Human Detection Robot Using PIR Sensor
  • PIR Sensor based Stepper Motor Control

PIR sensor can be used in many more projects we have given the example of some famous projects.