Basic Motion Sensor

// Things you need: arduino board, PIR motion sensor module (HC-SR501)

const int motionSensorPin = 2;
const int outputPin = 13;

void setup() {
  pinMode(outputPin, OUTPUT);
  pinMode(motionSensorPin, INPUT);
  Serial.begin(9600);
}

void loop() {
  int motionState = digitalRead(motionSensorPin);

  if (motionState == HIGH) {
    digitalWrite(outputPin, HIGH);
    Serial.println("Motion detected!");
  } else {
    digitalWrite(outputPin, LOW);
    Serial.println("No motion detected.");
  }

  delay(100);
}