int buzzer= 13;
int trigpin = 12;
int echopin = 11;

long duration;
int distance;

void setup() {
  //put your setup code here, to run once:
pinMode(trigpin, OUTPUT);
pinMode(echopin, INPUT);
pinMode(buzzer, OUTPUT);
Serial.begin(9600);
Serial.println("Ultrasonic Sensor HC-SRC04 Test");
Serial.println("with Arduino UNO R3");
}

void loop() {
  //put your main code here, to run repeatedly:
digitalWrite(trigpin, LOW);
 delayMicroseconds(2);
 digitalWrite(trigpin, HIGH);
 delayMicroseconds(10);
 digitalWrite(trigpin, LOW);
 duration = pulseIn(echopin,HIGH);
 distance = duration *0.034 / 2;
 
 Serial.print("distance: ");
 Serial.print(distance);
 Serial.println(" cm");

 if(distance <400 && distance>=200){
  tone (buzzer, 5000);
  delay(100);
  noTone(buzzer);
  delay(200);
 }

 if(distance <200 && distance>=100){
  tone (buzzer, 1000);
  delay(50);
  noTone(buzzer);
  delay(150);

 }
 if(distance <100 && distance>=2){
  tone (buzzer, 500);
  delay(50);
  noTone(buzzer);
  delay(100); }
}