What are these?

[k4kyv]

I have noticed lately that some of the consumer junk I bring home has a little white thing affixed with adhesive.  It is 1 3/4" long and about 3/8" wide, and has a bar code printed on it.  It is hollow like an envelope. I opened one up, and it contains two metallic strips, each one 1/4" wide and 1  7/16" long.

The latest one I found was attached to a page about middle way inside a paperback book I bought to-day.

I suspect it is some kind of anti-theft device.  Just wondering if anyone might know exactly what these are and how they work.

[w3jn]

passive anti-theft tag.  Google is your friend, there are many sites that explain how the various tags work.

[Jim, W5JO]

RFID tags.  That's why the cashier has a big magnet on the checkout stand, to neutralize them.

[NE4AM]

These are some neato magnetic technology.  There are actually two metal strips in the device.  One is a carbon steel strip, and one is an amorphous magnetic alloy.  The carbon steel is capable of being magnetized.  The amorphous alloy has a very square BH loop, and saturates at a very low field strength, a couple oersteads.

When you pass through the theft detection loops at the store exit, they are transmitting a LF wave, 125 kHz, if memory serves.  The amorphous strip saturates in response to the RF, and generates beaucoup harmonics, which the loop antenna detects. BEEP BEEP BEEP!

If the carbon steel strip becomes magnetized, its field will keep the amorphous strip saturated, so that the RF from the loops at the door cannot affect them and generate the harmonics.  When the check-out zombie waves the item over the well-worn spot on the counter, he/she is magnetizing the carbon steel so that you will be able to exit the store without the amorphous alloy strip setting off the detectors.

[k4kyv]

Sometimes after having paid for stuff those beepers go off anyway when I pass through the door carrying the merchandise and receipt.  I just ignore it and keep on going.  It's someone else's problem, not mine.  No-one has ever chased after me.  I wonder if the minimum-wage store clerks pay any attention to it; most likely they don't even GAF.

[Jim, W5JO]

Sometimes after having paid for stuff those beepers go off anyway when I pass through the door carrying the merchandise and receipt.  I just ignore it and keep on going.  It's someone else's problem, not mine.  No-one has ever chased after me.  I wonder if the minimum-wage store clerks pay any attention to it; most likely they don't even GAF.

Are you saying those greeters don't chase you down demanding to see the receipt?  I saw one in a wheelchair follow a woman to her car one time.