PIR Motion Sensor Alarm: DIY Home Security

A PIR (Passive Infrared) Sensor detects changes in infrared radiation, which occurs when a warm body (like a human) moves in its field of view. It's the same technology used in commercial motion-activated lights and alarms.

How PIR Sensors Work

The sensor contains a pyroelectric crystal that generates voltage when heated or cooled. A Fresnel lens in front focuses IR energy onto the sensor. When a person walks by, the sudden change in IR triggers an output signal.

Components

• Arduino Uno
• HC-SR501 PIR Sensor Module
• Buzzer
• LED
• (Optional) GSM Module for SMS alerts

Wiring

| PIR Pin | Arduino Pin | | :--- | :--- | | VCC | 5V | | GND | GND | | OUT | D2 |

Code

```cpp int pirPin = 2; int buzzerPin = 8;

void setup() { pinMode(pirPin, INPUT); pinMode(buzzerPin, OUTPUT); delay(30000); // Allow PIR to calibrate (30 seconds) }

void loop() { if (digitalRead(pirPin) == HIGH) { digitalWrite(buzzerPin, HIGH); delay(5000); // Alarm for 5 seconds digitalWrite(buzzerPin, LOW); } } ```

Adjustments

The HC-SR501 has two potentiometers:

• Sensitivity: How far it can detect motion.
• Time Delay: How long the output stays HIGH after detection.

Our Kit

Get started with the PIR Motion Sensor Alarm Using Arduino kit!