Now that you’ve blinked an LED, let’s build something more practical: a Motion Sensor Alarm. This project uses a PIR (Passive Infrared) sensor to detect movement and trigger a buzzer.

Components Required

Step 1: Wiring the Circuit

PIR Sensor Pins:

VCC → 5V on Arduino
GND → GND
OUT → Pin 2

Buzzer:

Positive (+) → Pin 8
Negative (-) → GND

Double-check connections before powering up.

Step 2: Upload the Code

Open the Arduino IDE and paste this:

int pirPin = 2;
int buzzer = 8;void setup() {
  pinMode(pirPin, INPUT);
  pinMode(buzzer, OUTPUT);
  Serial.begin(9600);
}void loop() {
  int motion = digitalRead(pirPin);  if (motion == HIGH) {
    digitalWrite(buzzer, HIGH);
    Serial.println("Motion detected!");
    delay(1000);
  } else {
    digitalWrite(buzzer, LOW);
    Serial.println("No motion");
  }
}

Click Upload ▶️

Step 3: How It Works

The PIR sensor detects heat changes (like a moving person)
When motion is detected, it sends a HIGH signal
Arduino turns on the buzzer
When there is no motion, the buzzer stays off

Important Notes

PIR sensors take 30–60 seconds to stabilize after power-on
You can adjust:
- Sensitivity (distance)
- Delay time (how long output stays HIGH)

These are controlled by the small knobs on the sensor.