Note: These are 125kHz key fobs (tags). If you want to add them to your lock system, please ensure that your system uses the same frequency of unencrypted 125kHz. Incompatible with other frequencies like 13.56MHz. Incompatible with encrypted tags like HID, Indala, Cobra, APCiK, Paradox, Radio, Honeywell, Kaba, Isonas, etc. Read only. Not rewritable. You cannot re-program them. Each key fob is already pre-programmed with a unique ID number. The 10-digit number is engraved on the tag casing. Each key fob is pre-programmed with a unique ID number. The 10-digit number is engraved on the tag casing. Compatible with other universal 125kHz tags like EM4100/4102. Suitable for 125kHz RFID proximity access control system and ID management system. For example, add it to your RFID door lock if applicable. Approx. Size: 1.4*1.1*0.2 inch. Casing Material: ABS Plastic. Color: Blue. Package includes 100 PCS.