This is a blank 13.56MHz RFID/NFC embedded in a phone charm - often used for train/bus passes but also found in other systems where a proximity card is desired. The tag contains a small RFID chip and an antenna, and is passively powered by the reader/writer when placed a couple inches away. These can be read by almost any 13.56MHz RFID/NFC reader but make sure it can handle ISO/IEC 14443 Type A cards as there are a few other encoding standards (like FeLica) They are tested and work great with both our PN532 NFC/RFID breakout board and Adafruit NFC/RFID Shield for Arduino! These chips can be written to & store up to 1 KB of data in writable EEPROM divided into banks, and can handle over 100,000 re-writes. You can use our PN532 NFC/RFID breakout board or Adafruit NFC/RFID Shield for Arduino to read and write data to the EEPROM inside the tag. There is also a permanent 4-byte ID burned into the chip that you can use to identify one tag from another - the ID number cannot be changed.These use a ISO/IEC 14443 Type A chipset, which used to be the 'classic' NFC chipset. In ~2014, the NFC forum decided not to support this chipset anymore, so newer phones do not support it. This only matters if you're trying to use this tag with a phone/tablet.Technical Details RFID chip specification: * 1 KiloByte (8 KiloBit) non-volatile EEPROM storage * Built in encryption engine with 48-bit key * 4 Byte unique identifier burned into the chip * 13.56 MHz frequency Tag specification: * 39.82mm x 24.85mm x 4mm * loop is 140mm/5.5" * 4.5 grams with loop, 4 grams without * Works about 1" away from RFID reader https://elecena.pl/product/22713784/13-56mhz-rfid-nfc-charm-classic-1k-discontinued 2023-03-06 https://elecena.pl/product/22713784/13-56mhz-rfid-nfc-charm-classic-1k-discontinued 2024-09-19