Arduino RFID Security System

#include <LiquidCrystal_I2C.h>
#include <SPI.h>
#include <MFRC522.h>
#include <Wire.h>
LiquidCrystal_I2C lcd(0x27, 16, 2);

unsigned long startMillis; //set up millis for reset
unsigned long currentMillis; //pull up millis for reset
const unsigned long period = 604800000; //the value is a number of milliseconds, ie 7 days

#define SS_PIN 10
#define RST_PIN 9
#define RELAY 3 //relay pin
#define BUZZER 2 //buzzer pin
MFRC522 mfrc522(SS_PIN, RST_PIN);   // Create MFRC522 instance.
void setup() {
  Serial.begin(9600);   // Initiate a serial communication
  SPI.begin();
  mfrc522.PCD_Init();
  pinMode(RELAY, OUTPUT);
  pinMode(BUZZER, OUTPUT);
  noTone(BUZZER);
  lcd.init();
  lcd.clear();
  lcd.backlight();
  tone(BUZZER, 1000);
  delay(100);
  noTone(BUZZER);
  lcd.print(F("ARDUINO SECURITY"));
  lcd.setCursor(0, 1);
  lcd.print(F("      DOOR  "));
  delay(2000);
  lcd.clear();
  lcd.print(F("   ACTIVATING    "));
  lcd.setCursor(0, 1);
  lcd.print(F("     SYSTEM    "));
  delay(2000);
  lcd.clear();
  digitalWrite(RELAY, HIGH);
  delay(2);
  digitalWrite(RELAY, LOW);
  lcd.print("   PLEASE BE ");
  lcd.setCursor(0, 1);
  lcd.print("    PATIENT  ");
  delay(2000);
  digitalWrite(RELAY, LOW);
  tone(BUZZER, 1000);
  delay(1000);
  noTone(BUZZER);
  lcd.clear();
  lcd.print("   SCAN CARD ");
  lcd.setCursor(0, 1);
  lcd.print("   TO UNLOCK  ");
}

void(*resetFunc) (void) = 0;

void loop() {
  currentMillis = millis();  //get the current "time" (actually the number of milliseconds since the program started)
  if (currentMillis - startMillis >= period)  //test whether the period has elapsed
  {
    resetFunc(); //call reset
  }
  if ( ! mfrc522.PICC_IsNewCardPresent())      return;   // Look for new cards
  if ( ! mfrc522.PICC_ReadCardSerial())    return;  // Select one of the cards
  Serial.print(F("UID tag :"));
  String content = "";
  byte letter;
  for (byte i = 0; i < mfrc522.uid.size; i++)
  {
    Serial.print(mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " ");
    Serial.print(mfrc522.uid.uidByte[i], HEX);
    content.concat(String(mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " "));
    content.concat(String(mfrc522.uid.uidByte[i], HEX));
  }
  Serial.println();
  content.toUpperCase();
  if ((content.substring(1) == "93 6D BE 0D")
      || (content.substring(1) == "51 67 DC B0")
      || (content.substring(1) == "A3 23 74 11") //change here the UID of the card/cards that you want to give access to
      || (content.substring(1) == "55 42 2B 0D"))
  {
    lcd.clear();
    lcd.backlight();
    lcd.print("     ACCESS     ");
    lcd.setCursor(0, 1);
    lcd.print("    GRANTED!    ");
    digitalWrite(RELAY, HIGH);
    tone(BUZZER, 1000);
    delay(400);
    noTone(BUZZER);
    delay(6600);
    digitalWrite(RELAY, LOW);
    lcd.clear();
    lcd.print("   SCAN CARD ");
    lcd.setCursor(0, 1);
    lcd.print("   TO UNLOCK  ");
  }

  else   {
    lcd.clear();
    lcd.backlight();
    lcd.print("     ACCESS     ");
    lcd.setCursor(0, 1);
    lcd.print("     DENIED     ");
    tone(BUZZER, 1000);
    delay(150);
    noTone(BUZZER);
    delay(25);
    tone(BUZZER, 1000);
    delay(150);
    noTone(BUZZER);
    delay(25);
    tone(BUZZER, 1000);
    delay(150);
    noTone(BUZZER);
    delay(25);
    tone(BUZZER, 1000);
    delay(150);
    noTone(BUZZER);
    delay(25);
    tone(BUZZER, 1000);
    delay(150);
    noTone(BUZZER);
    delay(1000);
    lcd.clear();
    lcd.print("   SCAN CARD ");
    lcd.setCursor(0, 1);
    lcd.print("   TO UNLOCK  ");
  }
}