WRITABLE and REWRITABLE: It's rewritable chip, and it can write in 125khz id format and H ID WG 125khz format. Suitable for making and back-up tags. FREQUENCY: 125kHz; Sensing Distance: 2.5 to 10 cm (1 to 4 inch); Data Storage Life: 10 Years. CHIPS: T5577 Chips, 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. MATERIAL: copper coil inside. Casing Material is ABS plastic. Waterproof and Durable. Package includes 50Pcs. 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. chip: ATMEL T5577 (The best rewritable chip) Working Mode: Read-write modes - Can be used in 125KHz RFID card Copier/ Duplicator Storage Capacity: 330 bit (264 free bit availability) Reading distance is 0 - 10cm Note: Please note it need to write the id on it before you read, it's chip. Colour:Black Material:plastic Package Contents: 50 x Key Fob Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is 1-3cm.