Usage Tips:WRITABLE & 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: High-Quality copper coil inside. Casing Material is ABS plastic. Waterproof & 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/ DuplicatorStorage Capacity: 330 bit (264 free bit availability)Reading distance is 0 - 10cmNote: Please note it need to write the id on it before you read, it's chip.Colour:BlackMaterial:plasticPackage Contents:50 x Key FobOnly 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.