void setup() {
  // put your setup code here, to run once:

}

void loop() {
  // put your main code here, to run repeatedly:

}
#define MOTION_SENSOR_PIN  2 // The Arduino Nano pin connected to the OUTPUT pin of motion sensor
#define LED_PIN            7 // The Arduino Nano pin connected to the LED

int motion_state      = LOW; // current  state of motion sensor's pin
int prev_motion_state     = LOW; // previous state of motion sensor's pin

void setup() {
  Serial.begin(9600);                // Initialize the Serial to communicate with the Serial Monitor.
  pinMode(MOTION_SENSOR_PIN, INPUT); // set arduino pin to input mode
  pinMode(LED_PIN, OUTPUT);          // set arduino pin to output mode
}

void loop() {
  prev_motion_state = motion_state;             // store old state
  motion_state  = digitalRead(MOTION_SENSOR_PIN); // read new state

  if (prev_motion_state == LOW && motion_state == HIGH) { // pin state change: LOW -> HIGH
    Serial.println("Motion detected!");
    digitalWrite(LED_PIN, HIGH); // turn on
  }
  else if (prev_motion_state == HIGH && motion_state == LOW) { // pin state change: HIGH -> LOW
    Serial.println("Motion stopped!");
    digitalWrite(LED_PIN, LOW);  // turn off
  }
}