It is a blank 13.56 MHz RFID/NFC sticker with a NTAG203 chip - often used for train/bus passes, information sharing, contactless payment, but also in other systems where a proximity card is desired. The label contains a small RFID chip and an antenna, and is passively powered by the reader/writer when placed a few cm away.

These can be read by almost any 13.56 MHz RFID/NFC reader, but make sure it can handle ISO/IEC 14443 Type A cards (the standard used by NTAG) as there are a few other coding standards (such as FeLica).

These chips can be written and store up to 144 bytes of data in an writable EEPROM divided into 4 byte banks, and can handle more than 10,000 rewrites. You can use the Adafruit NFC/RFID shield for Arduino to read and write data about the EEPROM inside the label. There is also a permanent 7-byte serial number engraved on the chip that you can use to identify one label from another - the identification number cannot be changed.

They use a NTAG chipset, a type 2 label that can be used with any smartphone. Unlike "Classic 1K" cards (alias MiFare S50s), these tags are more secure and work with almost all RFID-enabled phones since they avoid patent issues with Mifare, which requires an NXP chipset or a license.

Technical details

RFID chip specification :

    144 bytes of user r/w memory, divided into 36 pages (4 bytes each)
    7-byte unique identifier engraved in the chip
    Operating frequency: 13.56 MHz

Specification of the tags:

     40 mm x 25 mm x 1 mm
    5.3 grams / 0.2 oz
    Works about 4" away from reader