RFID based security or entrance systems are pretty common in many areas. Basically it is not considered very secure way of locking very important objects, but for low level security or staff registering it is ideal solution. JOJO have shared his simple build of RFID based door lock controlled by Arduino.
He used common RFID reader module which is accessed from Arduino via serial interface. Only single signal wire is needed as this is one way comm. Program is straight forward – tag IDs are stored in code as array, so if you need to add new or change tag, you need to reflash Arduino. Since this project is more tutorial than real life project it doesn’t activate anything, just keeps count of reads. It can be easily extended for your own needs by adding few lines of code.