int trigPin = 9;  
int echoPin = 10; 
int buzzerPin = 7;
void setup() {
  Serial.begin(9600);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(buzzerPin, OUTPUT);
}
void loop() {
  long duration, distance;
  digitalWrite(trigPin, 0);
  delayMicroseconds(2);
   digitalWrite(trigPin, 1);
  delayMicroseconds(10);
  digitalWrite(trigPin, 0);
  duration = pulseIn(echoPin, 1);
  distance = duration * 0.034 / 2;
  
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");
  if (distance < 50) {
    digitalWrite(buzzerPin, 1);
     tone(7, 262, 250); 
  } else {
    digitalWrite(buzzerPin, 0);
  }
  
  delay(500); 
}