CERAMIC MATERIAL - Sturdy, lightweight, waterproof, hypoallergenic, and no battery needed. TO BE USED WITH - an RFID Duplicator (sold separately) to create backup copies of key fobs and cards typically used for building access control. SIZE BEFORE YOU BUY - We suggest obtaining a ring sizer kit to assist in finding a comfortable size. T5577 125kHz CHIP - Can be reprogrammed numerous times