int trigPin = 13;
int echoPin =12;
const int buzzer = 7; 
float duration_us, distance_cm; 
void setup(){  
pinMode(buzzer,OUTPUT); // pin buzzer 
}  
void loop(){  

  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  
  duration_us = pulseIn(echoPin, HIGH);

  
  distance_cm = 0.017 * duration_us;

  if (distance_cm < 200) {
	 digitalWrite(buzzer, HIGH);
	   delay(4000);  
	 digitalWrite(buzzer, LOW); 
	   delay(4000);
	 }  
delay(100);   
}