Parallax RFID board
From HacDC Wiki
Setting the parallax RFID up is painfully simple. Just hook it up to a serial port at 2400,8,N,1 and you're off.
It's a simple device -- basically an RFID chip and a PIC used to interface with serial. The RFID chip EM4095 is designed for low-frequency, amplitude modulated transponders.
There's not much of an obvious way to hack into the thing because most all of the functionality (frequency generation, signal detection) is in the EM4095. I tried tapping the Demod Out pin to see if I could get any info that the PIC wasn't letting pass through.
I tried a variety of cards on the thing. Mostly-predictably, only the low-freq cards that it came with gave out anything that made sense.
Using one of the supplied cards spits out what a reasonably low-frequency data stream.
The only other card that got any response was the Zipcard, which sync'ed up with the RFID at 133kHz, but spat data that looks like the Zipcard's running at a much higher frequency -- probably a multiple of 133?
So basically, the parallax unit seems to be easy and reliable with its cards, but sadly not too hackable/expandable.