These are 13.56MHz key fobs (tags). If you want to register them to your lock system, please ensure that your system uses the same frequency 13.56MHz. Incompatible with other frequencies like 125kHz. Read-only. Not re-writable. Each key fob is already pre-programmed. You cannot re-program them by a card writer. Compatible with MIFARE Classic 1K Card (M1 Card). If your lock uses an M1 card, these key fobs work for your lock too. Suitable for 13.56MHz RFID proximity access control system and ID management system. For example, register them to your RFID door lock as new keys if applicable.