Security Tags

Discussion in 'General Electronics Chat' started by Duane P Wetick, May 8, 2010.

  1. Duane P Wetick

    Thread Starter Senior Member

    Apr 23, 2009
    Lately, I've been curious about those security scanners commonly used in libraries and department stores. It appears to be a long range metal detector and yet is in-sensitive to belt buckles, keys and other metal objects that one carries. I don't think that it is RFID technology. So what is it that gets interrogated by the scan antennas?

    Cheers, DPW [ Everything has limitations...and I hate limitations.]
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
    One system used metalic strips which emitted a weak RF burst when hit with a magnetic pulse. Strip placed in book spline.
  3. retched

    AAC Fanatic!

    Dec 5, 2009
    They are pretty neat. They are basically EM antenna that absorb a particular frequency. there is a weak magnet inside that augments or retards the shape of the antenna causing a short between legs of the antenna, allowing it to react in an allowable frequency. Degaussing, after the book is returned, re-sets the antenna to its non shorted, reactive frequency.

    The permanent reference books that are not allowed to be taken out of the library, have no ferrous short-creating shunt-type jammie in the tag, so it can not be "deactivated".

    Here you go, wikipedia has a pretty good page on the devices:
    Last edited: May 11, 2010