int buzzer = 13;               
int sensor = 4;               
int sensorState = LOW;             
int val = 0;                   
 
void setup() {
  pinMode(buzzer, OUTPUT);      
  pinMode(sensor, INPUT);     
  Serial.begin(9600);   
}
 
void loop(){
  val = digitalRead(sensor);                      
  if (val == HIGH) {                             
    digitalWrite(buzzer, HIGH);                 
    if (sensorState == LOW) {                  
      Serial.println("Motion detected!");     
      sensorState = HIGH;
    }
  } else {
    digitalWrite(buzzer, LOW);       
    if (sensorState == HIGH){           
      Serial.println("Motion ended!"); 
      sensorState = LOW;
    }
  }
}