On Wed, 10 Mar 2004 00:27:31 +1100, Jonathan Johnson
wrote:

> RFID would be pretty effective I think but it presents
a major problem in reliably containing the scan field
(try holding your wallet up to a prox card reader with
your card buried under 26 layers of cards and other crap
etc, most often it will still work. it penetrates pretty
damn well, which, in its normal situation is perfect.

That's because it's designed like that - it has an
effective field about 6" to 12" in diameter to make it
easier and more reliable to use for door-opening.  If
you built something yourself you'd use much less power
and much smaller coils to pick up the signal, limiting
it to, say 1" diameter or less.  The RFID device really
has to be "inside" the reader's coil to pick up its
activation power, so there shouldn't be much problem
with cross-reading, especially if you activate the
"scan" one square at a time.

Cheers,

Howard Winter
St.Albans, England

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