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Walmart security alram for DVDs and Ink cartridges — Parallax Forums

Walmart security alram for DVDs and Ink cartridges

mikedivmikediv Posts: 825
edited 2010-05-26 22:40 in General Discussion
Hey guys I bought some ink cartridges from Walmart last night when I was leaving I set off the alarm because the kid forgot to take my ink cartridges out of the plastic security box he let me have one to keep when I got home I pulled it apart it had a

small wire wound device with a capacitor soldered to the leads does this work anything like RFID I wanted to keep it so I could figure out what it does , it looks to me like it just triggers an alarm and has no intelligence is that right

photo attached
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Comments

  • John R.John R. Posts: 1,376
    edited 2010-05-26 01:26
    I was always under the impression that there was RFID involved, but I have no "inside knowledge" to be any more certain than you are.

    The cap could be for tuning, or could be to hold and release energy as a simple return "pulse" for the system. I'll be you could have some fun just carrying that thing through the doors in your shoe or someplace.

    Give the greeter some excitement for the night.

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    John R.
    Click here to see my Nomad Build Log
  • mctriviamctrivia Posts: 3,772
    edited 2010-05-26 01:42
    The security systems I have installed like that all used RFID. But that does not look like the tags used in any of them. They normally look like a flexible sticky pcb with a long trace rapping around it several times as an intena. at the center is a cap and tiny microcontroller though they are usually both potted over.

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  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2010-05-26 01:53
    A cap paralleled with an inductor forms a resonant tank circuit. Such a circuit can be detected in the presence of an RF field of the same frequency by measuring its energy absorption. For a reference, see this article:

    en.wikipedia.org/wiki/Grid_dip_oscillator

    -Phil
  • Peter KG6LSEPeter KG6LSE Posts: 1,383
    edited 2010-05-26 02:58
    Phil that was exactly what I was thinking of too....

    I have some large cans ( headphones) I wear all the time .. I have noticed how I get a loud "CLICK CLICK CLICK" when ever I go to wally world or My college library .

    Peter KG6LSE

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  • BradCBradC Posts: 2,601
    edited 2010-05-26 03:01
    Phil Pilgrim (PhiPi) said...
    A cap paralleled with an inductor forms a resonant tank circuit. Such a circuit can be detected in the presence of an RF field of the same frequency by measuring its energy absorption. For a reference, see this article:

    en.wikipedia.org/wiki/Grid_dip_oscillator

    Which is precisely how some of these devices work. There is no need for identification, so RFID is overkill. They just want to know if one is walking out the door. My old (old, old, old) analogue mobile phone had a resonant circuit in it somewhere that used to set off half the units in Perth if I walked into a shop with it. It started out as an annoyance, but in the end became quite good fun.

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  • Peter KG6LSEPeter KG6LSE Posts: 1,383
    edited 2010-05-26 03:27
    the next time I go to wally world I am takeing a Freq counter and a loop Ant .

    Peter KG6LSE

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    "Carpe Ducktum" "seize the tape!!"
    peterthethinker.com/tesla/Venom/Venom.html
    Never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway. —Tanenbaum, Andrew S.
    LOL
  • TubularTubular Posts: 4,705
    edited 2010-05-26 03:53
    I once did a few projects for a major shaving blade company. They told me those tags (in sticker form) cost them 4 cents each.
  • mctriviamctrivia Posts: 3,772
    edited 2010-05-26 14:37
    the problem with the CL circuit is you can't deactivate it. where the RFID can be turned off. not a problem for stuff never ment to leave the store attached to the product but it is a problem if they are meant to leave the store.

    i remember hearing that eventually manufacturers would like to stick RFID tags on every single product in the store. You could check out by running your cart through the detector and paying the total. they could also track products movements from manufacturing to dump.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Lots of propeller based products in stock at affordable prices.
  • bill190bill190 Posts: 769
    edited 2010-05-26 16:22
    At the following link is a similar device the Soviets made to eavesdrop on the U.S. Embassy in Moscow (no batteries needed!)...

    http://www.spybusters.com/Great_Seal_Bug.html
  • mikedivmikediv Posts: 825
    edited 2010-05-26 22:40
    Thanks guys . I did not think it looked like any RFID I had seen but I would think it would be a good idea ,, Sometimes in this particular store when you are checking out you here the alarm go off quite bit . Most of the time no one stops they just keep going and Walmart employees do nothing. I stopped because I knew the kid that checked me out and to be honest I wanted one.
    Anyway if they did RFID they could compare against inventory to see what is walking out the door. The worst is we now have these automatic check out counters you are suppose to scan your goods and then pay there is no one around I hate to say this but I often see people not scanning things in there carriages.. It would give them a good idea of why the inventory does not match sales. I did try to get this unit to emit something RF but even waving a magnet over it did not illicit any readings of course it could be the way I am trying to measure the output.
    Thanks Guys for the info
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