Description:
Current version of the 125 kHz, RFID reader for microcontrollers we have in stock comes from JsxzLz. It is very complete as it comes with an external antenna (you could also use your own antenna) and 3 free RFID tags!

This unit is compatible with any microcontroller that works on 5V, we have not yet tested this unit with 3.3V compatibility. When a card is brought close to the antenna, the serial code of the RFID tag is communicated via serial connection (9600 baud).

Resources:
Arduino Code including connection details.