If I have a low-frequency RFID passive tag (125 kHZ), how could I create another tag that, if interrogated by an RFID reader, would produce the same result as the original? And would they have the same serial number?
If the tags are read-write, you can write the same information (usually a serial number) to as many passive tags as you like, and they will respond with the same ID number.
There is no system for preventing the tags from having the same serial number. If the tags are read-only, then there is no way to have a tag respond with the same serial number, because the serial number would have been written into the tag.
—Mark Roberti, Founder and Editor, RFID Journal