Improved Arduino code from http://theifdark.blogspot.com/2014/07/arduino-rfid-card-door-lock-system-100.html

RFID_door

#include <SoftwareSerial.h>

#define CARD_CODE_LENGTH 10
const int ledPin = 2;
const int doorLock = 4;
const int txPin = 6;
const int rxPin = 8;

int byteRead = 0;
int bytesRead = 0;
int wrong = 0;

char code[CARD_CODE_LENGTH+1] = {0}; // +1 for the null terminator used when printing the code
const char availableCodes[][CARD_CODE_LENGTH+1] = {
  "XXXXXXXXXX",
  "XXXXXXXXXX"
};
const int numberOfCodes = sizeof(availableCodes)/sizeof(availableCodes[0]);

void setup()  {
  Serial.begin(9600);

  pinMode(ledPin, OUTPUT);
  digitalWrite(ledPin, LOW);
  pinMode(doorLock, OUTPUT);
  digitalWrite(doorLock, LOW);
}

void loop()  {
  SoftwareSerial RFID = SoftwareSerial(rxPin,txPin);
  RFID.begin(2400);

  if(RFID.read() == 10) { // I'm not sure what this refers to. This would imply all of the cards start with the number 10 which is the Line feed character
    bytesRead = 0;
    while(bytesRead<CARD_CODE_LENGTH) {
      byteRead = RFID.read();
      if((byteRead == 10)||(byteRead == 13)) { // Same as above. If they do refer to the characters, replace them with '\n' or '\r' respectively
        break;
      }
      code[bytesRead] = byteRead;
      bytesRead++;
    }
    if(bytesRead == CARD_CODE_LENGTH) {
      checkCard();
    } else {
      wrongCard();
    }
  }
}

void checkCard()  {
  for(int i=0; i<numberOfCodes; i++) {
    Serial.print(availableCodes[i]);
  }
  
  Serial.print("Card read: ");
  Serial.println(code);
  
  for(int i=0; i<numberOfCodes; i++) {
    if(codeMatches(code, availableCodes[i])) {
      rightCard();
    }
  }
  wrongCard();
}

boolean codeMatches(const char codeA[11], const char codeB[11]) {
  for(int i=0; i<CARD_CODE_LENGTH; i++) { // Don't check the null terminator since it doesn't matter
    if(codeA[i] != codeB[i]) {
      return false;
    }
  }
  return true;
}

void rightCard()  {
  digitalWrite(ledPin, HIGH);

  digitalWrite(doorLock, HIGH);
  delay(5000);
  digitalWrite(doorLock, LOW);

  digitalWrite(ledPin, LOW);
}

void wrongCard()  {
  Serial.print("Wrong Card");
  Serial.println("");
  delay(300);
  digitalWrite(ledPin, HIGH);
  delay(300);
  digitalWrite(ledPin, LOW);
  delay(300);
  digitalWrite(ledPin, HIGH);
  delay(300);
  digitalWrite(ledPin, LOW);
  delay(300);
  digitalWrite(ledPin, HIGH);
  delay(300);
  digitalWrite(ledPin, LOW);
}