[RFI] Wal-Mart to Put Radio Tags on Clothes - WSJ.com

[Andy]

I'm not very knowledgeable about RFID tags, which is what I think
these are.  But my understanding is that RFID devices have no internal
power; they get their power from the nearby scanner, and otherwise
can't transmit anything.

But I think I've not actually seen one either.  The theft-deterrent
tags I've seen (and taken apart) on purchased items in the past, had
no apparent active circuitry such as an IC in them and seemed to be
just a tuned circuit of some sort.  (I'm sure this shows my ignorance
about them.  Someone will probably point out that they also had
something like a diode, which I didn't see.)

> BTW:  Is an aluminumized static bag sufficient to shield credit
> cards and driver's licenses from undesired scanning or is something
> more robust required?

Good question.  For ordinary credit cards without a smart IC, they use
a magnetic strip, and a static bag provides little if any shielding to
magnetic fields unless it's mu-metal or some other magnetic material,
which I'm sure they aren't.  On the other hand, you've got to be
really close to the magnetic strip to read it.

I really don't know if they shield RFID type signals.  I thought the
conductive substance is a very poor conductor, and rather thin, so it
might not do much to the RF.

My driver's license has optical scan codes on it (1D and 2D barcodes)
and I think that's it.

Andy