const int trigPin = 3;
const int echoPin = 2;
const int buzzerPin = 13;

void setup() {
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(buzzerPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  digitalWrite(trigPin, LOW);  
  delayMicroseconds(2); 

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

  long duration = pulseIn(echoPin, HIGH);

  int distance = duration * 0.034 / 2;

  if (distance < 10) {
    tone(buzzerPin, 1000);
    delay(50);
    noTone(buzzerPin);
    delay(1);
  } else if (distance < 20) {
    tone(buzzerPin, 1000);
    delay(200);
    noTone(buzzerPin);
    delay(80);
  } else if (distance < 30) {
    tone(buzzerPin, 1000);
    delay(300);
    noTone(buzzerPin);
    delay(300);
  } else {
    noTone(buzzerPin);
  }

  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");
  delay(500);
}