This is a MiFare Classic card - often used for electronic locks or customer identification. The tag contains an NXP S50 chip and an antenna and is passively powered by the reader/writer when placed a couple of inches away.

Specifications

• 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

Useful links

• Wikipedia MIFARE