WRITABLE & REWRITABLE: It's rewritable chip, and it can write in 125khz id format and H ID WG 125khz format. Suitable for making new and back-up tags. | CHIPS: ATMEL T5577 (compatible with other universal 125kHz tags), it doesn't have pre-programmed id number, so need to write the id on it before you read, so make sure you have the writer before you buy it. | NOTE: You cannot add them to RFID locks directly. You must write data into them by a 125kHz RFID card writer before use. They are blank tags, no data inside. Can write by 125KHz RFID writer/copier,CAN NOT WORK WITH ONITY SYSTEM and Proxmark3 RDV4. NOT NFC CHIP,Can't work with NFC Phone. | FREQUENCY: 125kHz; Sensing Distance: 2.5 to 10 cm (1 to 4 inch); Data Storage Life: 10 Years. | MATERIAL: High-Quality copper coil inside. Casing Material is ABS plastic. Waterproof & Durable.