code.c

#include <MFRC522.h>
#include <LiquidCrystal_I2C.h>
#include <Keypad.h>
#include <SoftwareSerial.h>
#include <Servo.h>
#include <SPI.h>
SoftwareSerial SIM800(3, 4);
MFRC522 mfrc522(10, 9);
LiquidCrystal_I2C lcd(0x27, 16, 2);
Servo sg90;
constexpr uint8_t greenLed = 7;
constexpr uint8_t redLed = 6;
constexpr uint8_t servoPin = 8;
constexpr uint8_t buzzerPin = 5;
char initial_password[4] = { '1', '2', '3', '4' };
String tagUID = "C3 31 49 E2";
char password[4];
boolean RFIDMode = true;
boolean NormalMode = true;
char key_pressed = 0;
uint8_t i = 0;

const byte rows = 4;
const byte columns = 4;
// Keypad pin map
char hexaKeys[rows][columns] = {
  { '1', '2', '3', 'A' },
  { '4', '5', '6', 'B' },
  { '7', '8', '9', 'C' },
  { '*', '0', '#', 'D' }
};

byte row_pins[rows] = { 2, 1, 0};
byte column_pins[columns] = { A0, A1, A2,A3 };

Keypad keypad_key = Keypad(makeKeymap(hexaKeys), row_pins, column_pins, rows, columns);
void setup() {

  pinMode(buzzerPin, OUTPUT);
  pinMode(redLed, OUTPUT);
  pinMode(greenLed, OUTPUT);
  sg90.attach(servoPin);
  sg90.write(0);
  lcd.init();
  lcd.backlight();
  SPI.begin();
  mfrc522.PCD_Init();
  SIM800.begin(9600);
  SIM800.print("AT+CMGF=1\r");
  delay(100);
  SIM800.print("AT+CNMI=2,2,0,0,0\r");
  delay(100);
  lcd.clear();
}
void loop() {
  if (NormalMode == false) {
    receive_message();
  } else if (NormalMode == true) {
    if (RFIDMode == true) {
      receive_message();
      lcd.setCursor(0, 0);
      lcd.print("   Door Lock");
      lcd.setCursor(0, 1);
      lcd.print(" Scan Your Tag ");
      if (!mfrc522.PICC_IsNewCardPresent()) {
        return;
      }
      if (!mfrc522.PICC_ReadCardSerial()) {
        return;
      }
      String tag = "";
      for (byte j = 0; j < mfrc522.uid.size; j++) {
        tag.concat(String(mfrc522.uid.uidByte[j] < 0x10 ? " 0" : " "));
        tag.concat(String(mfrc522.uid.uidByte[j], HEX));
      }
      tag.toUpperCase();
      if (tag.substring(1) == tagUID) {
        lcd.clear();
        lcd.print("Tag Matched");
        lcd.clear();
        lcd.print("Enter Password:");
        lcd.setCursor(0, 1);
        RFIDMode = false;
      } else {

        lcd.clear();
        lcd.setCursor(0, 0);
        lcd.print("Wrong Tag Shown");
        lcd.setCursor(0, 1);
        lcd.print("Access Denied");
        digitalWrite(buzzerPin, HIGH);
        digitalWrite(redLed, HIGH);
        send_message("Someone Tried with the wrong tag \nType 'close' to halt the system.");
        delay(3000);
        digitalWrite(buzzerPin, LOW);
        digitalWrite(redLed, LOW);
        lcd.clear();
      }
    }

    if (RFIDMode == false) {
      key_pressed = keypad_key.getKey();
      if (key_pressed) {
        password[i++] = key_pressed;
        lcd.print("*");
      }
      if (i == 4) {
        delay(200);
        if (!(strncmp(password, initial_password, 4))) {
          lcd.clear();
          lcd.print("Pass Accepted");
          sg90.write(90);
          digitalWrite(greenLed, HIGH);
          send_message("Door Opened \nIf it was't you, type 'close' to halt the system.");
          delay(3000);
          digitalWrite(greenLed, LOW);
          sg90.write(0);
          lcd.clear();
          i = 0;
          RFIDMode = true;
        } else {
          lcd.clear();
          lcd.print("Wrong Password");
          digitalWrite(buzzerPin, HIGH);
          digitalWrite(redLed, HIGH);
          send_message("Someone Tried with the wrong Password \nType 'close' to halt the system.");
          delay(3000);
          digitalWrite(buzzerPin, LOW);
          digitalWrite(redLed, LOW);
          lcd.clear();
          i = 0;
          RFIDMode = true;
        }
      }
    }
  }
}

void receive_message() {
  char incoming_char = 0;
  String incomingData;

  if (SIM800.available() > 0) {
    incomingData = SIM800.readString();
    delay(10);
  }
  if (incomingData.indexOf("open") >= 0) {
    sg90.write(90);
    NormalMode = true;
    send_message("Opened");
    delay(10000);
    sg90.write(0);
  }
  if (incomingData.indexOf("close") >= 0) {
    NormalMode = false;
    send_message("Closed");
  }
  incomingData = "";
}

void send_message(String message) {
  SIM800.println("AT+CMGF=1");
  delay(100);
  SIM800.println("AT+CMGS=\"+91xxxxxxxxxx\"");
  delay(100);
  SIM800.println(message);
  delay(100);
  SIM800.println((char)26);
  delay(100);
  SIM800.println();
  delay(1000);
}