constexpr byte LED1 = 3;
constexpr byte Level1 = A0;
constexpr byte Buzzer = 2;
constexpr byte Button = 9;
int buttonState = 0;
boolean BuzzerState = false;

unsigned long startMillis;
unsigned long currentMillis;
unsigned long period = 0;
const unsigned long wantedPeriod = 4000;

void setup() {

  pinMode(LED1, OUTPUT);
  pinMode(Level1, INPUT);
  pinMode(Button, INPUT);
  pinMode(Buzzer, OUTPUT);
  Serial.begin(115200);
  startMillis = millis();
}

void loop() {

  buttonState = digitalRead(Button);
  BuzzerState = false;

  if (digitalRead(Level1) == HIGH) {
    digitalWrite(LED1, HIGH);
    BuzzerState = true;
  } else {
    digitalWrite(LED1, LOW);
  }

 if (digitalRead(Button) == HIGH) {
        startMillis = millis();
        // This makes sure that the delay will become valid
        // after the first button press! 
        period = wantedPeriod;
  }

  
  if (millis() - startMillis < period) {
    BuzzerState = false;
  }

  if (BuzzerState == true) {
        digitalWrite(Buzzer, HIGH);
  } else {
       digitalWrite(Buzzer, LOW);
  }
}