const int gasSensor = A0;
const int buzzer = 8;

void setup() {
  pinMode(buzzer, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  int gasValue = analogRead(gasSensor);

  Serial.println(gasValue);

  if (gasValue > 400) {
    tone(buzzer, 1000);
  } else {
    noTone(buzzer);
  }

  delay(100);
}