const int motion_pin = 9;
int last_state = LOW; 
void setup(){
  Serial.begin(9600);
  pinMode(motion_pin,INPUT);
}
void loop(){
  int isMotionDetected = digitalRead(motion_pin);
  if(isMotionDetected == HIGH && last_state == LOW){
    Serial.println("motion detected");
  }
  else if(isMotionDetected == LOW && last_state == HIGH){
    Serial.println("Motion Disappeared");
  }
  last_state = isMotionDetected;
}