Pack of 20 changeable UID NFC 1K S50 cards, stickers and keyfobs for Android MCT app use. These CUIDtype 13.56 MHz tags allow the Sector 0 Block 0 UID to be reprogrammed for legitimate testing, replacement, or development tasks. Key benefits Changeable UID: Block 0, the serial number manufacturers block, can be programmed to a custom UID for system testing, device provisioning, or tag replacement. Compatible write methods: UID can be modified directly using compatible MIFARE readwrite devices or via an Android phone running the MCT modify UID app. Reliable performance: 1 kbyte EEPROM memory, 100,000 rewrite cycles, and up to about 10 cm read distance depending on the reader. Main specifications Chip type: CUID Frequency: 13.56 MHz Protocol: ISO14443A Memory: 1 kbyte EEPROM Rewrite endurance: 100,000 times Read distance: 0 to 10 cm depending on reader Material: PVC Form factor: card, sticker, or keyfob options; diameter for keyfob tag 25 mm Initial key: FFFFFFFFFFFF (12 F) Pack quantity: 20 pieces Important notes Block 0 (UID block) is writable and can be modified with compatible tools or the MCT Android app. Many common 13.56 MHz rfid readers and standard NFC phone apps cannot write these particular cards without the appropriate write tool or app. Small enough to fit on a key ring and available with an external number for easier identification. Color variation may occur due to monitor differences. Typical use scenarios Access control testing and commissioning: program test UIDs when verifying reader and controller behavior without changing production tags. System development and debugging: assign specific UIDs for software development, QA, and integration testing in access, payment simulation, or inventory projects. Replacement tags and event management: issue reprogrammable tags for temporary access, visitor badges, or product trials where UIDs need to be set to specific values. Compatibility and performance Works with ISO14443A compliant readers and devices that support writing the CUID block 0 with the correct tools. Read range and write capability depend on the reader hardware and environmental factors. This product provides a practical solution for developers, integrators, and installers who need reprogrammable UID tags for controlled, lawful testing and replacement tasks.