gasDetector.cpp

const int smokeSensorPin = A0;
const int buzzerPin = 9;
const int currentLevel = 0;

void setup() {
  Serial.println("Running ...");

  pinMode(buzzerPin, OUTPUT);
  pinMode(smokeSensorPin, INPUT);
  Serial.begin(9600);
}

void loop() {
  int smokeLevel = analogRead(smokeSensorPin);

  Serial.print("Smoke level: ");
  Serial.println(smokeLevel);

  if (smokeLevel > 700) {
    alarmLevel3();
  } else if (smokeLevel > 600) {
    alarmLevel2();
  } else if (smokeLevel > 500) {
    alarmLevel1();
  } else {
    digitalWrite(buzzerPin, LOW);
  }
}

void alarmLevel1() {
  for (int i = 0; i < 3; i++) {
    digitalWrite(buzzerPin, HIGH);
    delay(500);
    digitalWrite(buzzerPin, LOW);
    delay(500);
  }
}

void alarmLevel2() {
  for (int i = 0; i < 3; i++) {
    digitalWrite(buzzerPin, HIGH);
    delay(250);
    digitalWrite(buzzerPin, LOW);
    delay(250);
  }
}

void alarmLevel3() {
  digitalWrite(buzzerPin, HIGH);
}