This 125kHz RFID tag has a unique 32-bit ID code and can't be re-programmed. You can read the codes on the tags with a 125kHz RFID reader, such as the ID-12 or the ID-20, sold separately. Note: This is a with blank, unbranded RFID card. Includes: 1x 125kHz RFID Cards Features: EM4001 ISO based RFID IC 125kHz Carrier 2kbps ASK Manchester encoding 32-bit unique ID 64-bit data stream [Header+ID+Data+Parity] Dimensions: Each card is 2.13 x 3.35 x 0.03" (54 x 85.5 x 0.8mm) Quickstart Guide: https://www.sparkfun.com/tutorials/290