This is a basic RFID Tag Keyfob used for presence sensing , Access control etc. Works in the 125kHz RF range.
These tags come with a unique 32-bit ID and are not re-programmable. Tag is blank, smooth, and mildly flexible.
RFID Tag Keychain (125kHz) Features:
EM4001 ISO based RFID IC
32-bit unique ID
64-bit data stream [Header+ID+Data+Parity]