Can anyone tell me what this is ?

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elockpicker

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Hi,

Today I was at the library and found this (the picture is included).
I think this is used as the security system (anti shoplifting) ,It looks like an inductor ?
Can anyone please tell me what it is ?

Thank you very much.
 

Have you been living under a rock? Those things have been around for decades. That take a low frequency RF signal and double its frequency--theft detection.
 

Thank you very much,can you introduce some resources or give me some clues (I don't know any names; 'frequency doubler' ???) so I can know more about these things ?
 

Hi,
Its name is: RFID or "Tag"...
It exist in much versions, but these one hase possibly a workfrequency of 13.56 MHz, usual their dont make frequency doublig for answering, but has Amplitude Modulation or others coded answer...
The smallest ones hase a diameter of ca. 6mm, up to ca. 40x80mm, but you can find newst versions with "on chip antenna"_ca. 2.0x1.5-2.0mm
K.
 

It's an EAS (electronic article surveilance) tag, not RFID. It sends no codes. See:
 

Its just an LC circuit tunned to some specific frequency. Basically its a capacitor connected across a coil..Cheers
 

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