int trigPin = 9; 
int echoPin = 10; 
float duration_us, distance_cm;

void setup() {
 Serial.begin (9600);
 pinMode(trigPin, OUTPUT);
 pinMode(echoPin, INPUT);
}
void loop(){ 
 digitalWrite(trigPin, HIGH);
 delayMicroseconds(10);
 digitalWrite(trigPin, LOW);
 duration_us = pulseIn(echoPin, HIGH);
 distance_cm = 0.017 * duration_us;

Serial.print("distance: ");
Serial.print(distance_cm);
Serial.println(" cm");
tone(13,2000,100);
delay(duration_us/20);

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

duration_us = pulseIn(echoPin, HIGH);
distance_cm = 0.017 * duration_us;

Serial.print("distance: ");
Serial.print(distance_cm);
Serial.println(" cm");
noTone(13);
delay(duration_us/20);
}