Project:RFID Reader Writer
You can find the RFID module on ebay around £12.50 - £14
I bought the one below but it looks like it run out of stocks
Source Code : http://www.rcubestation.com/drivers/rfidcardset_sample.zip
The one below is the same from another vendor
This is a brief description the module
This is the Radio Frequency Identification (RFID) 13.56 Mhz module Kit Reader and Writer
The RFID Reader Module can be used in a wide variety of hobbyist and commercial applications, including access control, automatic identification, robotics, navigation, inventory tracking, payment systems, and car immobilization.
The reference PDF dcoument for RC522 chip : Download RC522.pdf
Basic on the Philips MFRC522 Chip
Power Voltage : 3.3V
Operating frequency: 13.56MHz
Read Range: 0 ~ 60mm (mifare1 card)
Dimensions: 40mm × 60mm
You will need MIFARE compatible rfid cards (tokens or labels as well).
Oyster uses mifare cards and is migrating from MIFARE Classic to MIFARE DESFire EV1.
MIFARE is the NXP Semiconductors-owned trademark of a series of chips widely used in contactless smart cards and proximity cards. According to the producers, billions of smart card chips and many millions of reader modules have been sold. The technology is owned by NXP Semiconductors (spin off from Philips Electronics in 2006) with headquarters in Eindhoven, Netherlands, and main business sites in Nijmegen, Netherlands, and Hamburg, Germany.
The MIFARE name covers proprietary technologies based upon various levels of the ISO/IEC 14443 Type A 13.56 MHz contactless smart card standard. For more information check out MIFARE page on wikipedia.
Good to read the rfid nfc page.
I learnt the internal workings of the mifare cards on mifare page on ladyada web site
to be able to read and write to cards with ardiuno.