The microcontroller AT89S52 is used here. 125khz RFID reader with TTL output is connected to the microcontroller. The TAG ids are stored in the microcontroller program, so you cant change it later. If you want to change then you should flash the code again.
The continuously reads the TAG id using the RFID reader, and if the tag id matches then the corresponding device will be toggled. If a wrong tag is shown for more than 2 times then the alarm is switched ON, until a programmed tag is shown.