We have been asked before if RFID identity numbers can be modified. From what I can tell, RFID tags are assigned sequential identification numbers that are permanently burned into the chip. I wasn’t really able to find any examples where one could program their own ID number. However, there is a caveat and details I should mention that might make it abundantly clear that most (if not all) RFID tags will never have duplicate information. Let’s take a look at an example part number that has a card design.
Parallax Part 28141
DigiKey part number 28141-ND is a read-only 125kHz RFID card. The datasheet indicates on page 2 that there are going to be 240 possible combinations for this particular tag. This is a staggering 1,099,511,627,776 unique numbers. It isn’t possible to modify this number, however, the chance there would ever be duplicated data is practically impossible. The manufacturer would have to sell more than that to make that possible. Let’s say theoretically they did manage to sell that many, Parallax could easily start over and there would still a very small chance there would ever be a duplicate in the same factory setting. Even if IDs somehow were duplicated across companies, it is unlikely to cause issues due to different use cases.
Are there configurable tags?
Some parts actually do have read/write setups, but not in the way you think. From what I could find, there is going to be a number of bytes that are writeable and the ID is still going to be hard-coded or pre-burned into the chip already. An example part number would be 1528-2798-ND (manufacturer part number 4034) made by Adafruit. This part’s datasheet says the chip can be written to and store up to 144 bytes of data on the writable EEPROM that can handle over 10k re-writes. The chip also has a permanent 7-byte serial number that cannot be changed. This configuration still allows a ton of unique ID’s as well as having some amount of customizability to contain user data. One could make a more unique identification scheme for an application that requires some amount of metadata stored on these kinds of RFID cards. You could even make your own sort of pseudo-ID by making your own generation scheme and writing to that user data.