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I noticed that when I pass the alarm gates in my library (the ones that beep when you bring a book through) I hear a high pitched buzz in my earbuds. When I take my earbuds off, I hear nothing. I'd like to exploit this property (whatever it may be) for the purposes of an art project. Does anyone know what causes this? I ask because I can't find much information about 'alarm gates earbuds buzz' online.

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    There's more signals out there than you know and thats why you need to have good protection on your cord. Its static of some kind. More than that I cant say right now :( – user6471 Nov 21 '13 at 3:26
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Basically your earbuds' cables act as an antenna and pick up the RF signal sent out by the gates to check for tags passing (which when present cause a specific signal to be picked up by the receiver in the gates which in turn triggers the alarm).

For more information you can check http://electronics.howstuffworks.com/everyday-tech/anti-shoplifting-device3.htm

To "exploit" this all you need is a radio transmitter and a receiver ;)

Hope this helps.

  • Thanks for the help. I'll update this post with the results of my experiments. – Miles Nov 21 '13 at 15:35
  • FWIW, this is also how the radio works on a Walkman without a visible antenna but your boombox needs that extendy metal thing to work well; the Walkman is actually using the headphone cable as an antenna. – lc. Nov 27 '13 at 0:39
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The same thing happens to me, but it only happens in my local library (in Cardiff), not in shops. I'm guessing that the security tags in library books differ from those found on clothes in a shop as they require activation and deactivation rather than removal.

The odd thing is that when it happened my first thought was essentially "I'd like to exploit this property (whatever it may be) for the purposes of an art project."

  • Great to see I'm not the only one! I'll let you know what I discover if this turns into a project. – Miles Nov 21 '13 at 15:34

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