#define PIN_TRIG 2
#define PIN_ECHO 3
#define buzz 12

void setup() {
  Serial.begin(9600);
  pinMode(PIN_TRIG, OUTPUT);
  pinMode(PIN_ECHO, INPUT );
  pinMode(buzz, OUTPUT );
}
void loop(){
  Serial.println(Ultrasonic());
  int cm = Ultrasonic();
  if (cm < 18 && cm != 0){
  digitalWrite(buzz, HIGH);
  delay(100);
  digitalWrite(buzz, LOW);
  delay(100);
  tone(buzz,300,1000);
  }
  else{
    digitalWrite(buzz,HIGH );
  }
  }
  int Ultrasonic(){
  long duration, distance;
  digitalWrite(PIN_TRIG,LOW);
  delayMicroseconds(2);
  digitalWrite(PIN_TRIG,HIGH );
  delayMicroseconds(10);
  digitalWrite(PIN_TRIG,LOW);
  duration = pulseIn(PIN_ECHO,HIGH );
  distance = duration / 58;
  return distance;
}