After seeing a similar project, Doug Cameron went ahead and reproduced his own universal RFID key as a challenge and form of entertainment. A universal RFID key is a device that can emulate other cards that operate on the same frequency, in this case 125 kHz. Using the onboard keypad, one simply enters the number of the RFID card to emulate, then present the universal key to the reader. Doug's project is an interesting example of not only understanding the theory behind RFID but also a lot of nefarious fun, while showing the weaknesses of RFID entry systems.
Doug has provided the schematic, Arduino sketch and detailed construction notes so you can make your own universal key - so visit his Instructable to learn how. And for more, we're on twitter and Google+, so follow us for news and product updates as well.
If you're wanting to experiment with your own Arduino-compatible circuits, then you'll need a an ATmega328P MCUs with Arduino Uno bootloader:
This is the same Atmel AVR ATmega328P microcontroller used in the official Arduino Uno, as well as our Eleven, EtherTen, USBDroid, and other boards. Perfect for building your own Arduino-compatible project directly on a breadboard or on a custom PCB, or for replacing the MCU in an existing board. Comes with the Arduino Uno bootloader pre-installed. Better still, it even has a special label stuck on top with details of the pinout, so you don't even need to look up the datasheet when connecting it up in your project! For more information and to order, click here!