Simple concept: read RFID tags from Parallax's RFID reader using PASM. It can check them against a known list of tags, or just output the tag. It can also disable or enable the reader with a simple method interface.
The list of tags can be in the child object, the parent object, or determined and supplied at run-time.
It has been tested at frequencies as low as 5MHz and as high as 100MHz with no problems.