This is a blank MiFare Classic tag embedded in a phone charm. These tags are like those often used for train/bus passes but also found in other systems where a proximity card is desired. The tag contains a NXP S50 chip and an antenna, and is passively powered by the reader/writer when placed a couple inches away. Since this tag has a small antenna, it has to be closer to the antenna than, say, a large credit-card sized tag.
These can be read by almost any 13.56MHz RFID/NFC reader but make sure it can handle MiFare 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.
S50 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
39.82mm x 24.85mm x 1mm
loop is 140mm/5.5″
2.63 grams with loop, 1.63 grams without
Works about 1″ away from RFID reader