#define buzzer 9
#define PIN_TRIG 7
#define PIN_ECHO 8

void setup() {
  Serial.begin(115200);
  pinMode(9, OUTPUT);
  pinMode(PIN_TRIG, OUTPUT);
  pinMode(PIN_ECHO, INPUT);

}

void loop() {
  digitalWrite(PIN_TRIG, HIGH);
  delayMicroseconds(10);
  digitalWrite(PIN_TRIG, LOW);

  int dist = pulseIn(PIN_ECHO,HIGH);
  Serial.print("Distance in CM:");
  Serial.println(dist/58);
  
  
  if (dist/58 <= 100){
    digitalWrite(buzzer, HIGH);
    delay(500);
    digitalWrite(buzzer, LOW);
  }
  else {
  digitalWrite(buzzer, LOW);
  }

  delay(1000);
}