const int magnet_switch = 2;     // Magnet switch
const int Buzzpin =  13;      // LED pin
unsigned long previousMillis = 0;
unsigned long interval = 15000;

void setup() {
  // initialize the LED pin as an output:
  pinMode(ledPin, OUTPUT);
  // initialize the pushbutton pin as an input:
  pinMode(magnet_switch, INPUT_PULLUP);

  Serial.begin(9600);
}

void loop() {

 unsigned long currentMillis = millis();
  if(digitalRead(magnet_switch) == HIGH ){
    if (currentMillis - previousMillis > interval) {
      digitalWrite(Buzzpin,HIGH);
    previousMillis = currentMillis;
     }    
  }else{
    Serial.println("OK");
  }
  // if (digitalRead(magnet_switch) == LOW) {
//     Serial.println("Switch Closed");
//     digitalWrite(ledPin, HIGH);
//     while (digitalRead(magnet_switch) == LOW) {}
//   }
//   else {
//     digitalWrite(ledPin, LOW);
//   }
// } 
}