int pirPin = 4;    // PIR sensor output connected to digital pin 4  
int ledPin = 13;   // LED connected to digital pin 13

void setup() {
  pinMode(pirPin, INPUT);   // Set PIR pin as input
  pinMode(ledPin, OUTPUT);  // Set LED pin as output
  Serial.begin(9600);       // Initialize serial communication at 9600 bps
}

void loop() {
  int pirState = digitalRead(pirPin);  // Read PIR sensor state
  if (pirState == HIGH) {              // If motion is detected
    digitalWrite(ledPin, HIGH);        // Turn on LED
    Serial.println("Motion detected!"); // Print message to serial monitor
    delay(1000);                       // Wait for 1 second
  } else {                             // If no motion is detected
    digitalWrite(ledPin, LOW);         // Turn off LED
  }
}