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Thread: "Chip" Keys

  1. #1 "Chip" Keys 
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    (Maybe belongs in General category?). Ten years ago, we bought a used Ford Explorer, a '95 model. Learning fast, I found it had the recognizable by computer (PCM, in automotive jargon) ignition key. Not sure if it communicated, yet, wirelessly, which meant that a savvy thief could still hot-wire around the remarkable keys.

    The idea is that, by immobilizing the PCM function, the only way to steal the vehicle is to get it on a truck or trailer. Cannot be steered unless the ignition switch is turned to unlock the steering wheel, that allowing the transmission shifter to be placed out of "Park" position.

    The factory-supplied keys in '95 were "programmed" at the factory; admonitions were posted cautioning against losing them, as only Dealers could make new ones, at exhorbitant cost, of course. Today, the ACE hardware store near our house has a large sign proclaiming "We Make Chip Keys".

    So, how does the computer communicate with the key inserted into the ignition switch? What sort of unique identifying means is employed allowing zillions of keys fitting similar vehicles to disallow cross-use? jocular


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    Forum Radioactive Isotope MagiMaster's Avatar
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    You only need 36 bits of ID to have about 10 unique numbers for every person on the planet, so if the key can communicate just 36 blips to the locking system it'd be able to do the job. (They probably use more bits than that though.) I don't actually know the details of how the keys transmit those bits though, but I imagine it's something similar to how RFID works. In RFID, the reader supplies the power in the form of a radio wave which the RFID tag echos back in a certain pattern.


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  4. #3  
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    Quote Originally Posted by jocular View Post
    So, how does the computer communicate with the key inserted into the ignition switch? What sort of unique identifying means is employed allowing zillions of keys fitting similar vehicles to disallow cross-use? jocular
    Once you know a single code that was transmitted by a transponder key (which you can get from just reading the key electronically) AND you know the algorithm used to generate the next code (which you must get from the manufacturer) then you can re-create the key sequencing that a keyfob uses.

    The key copier reads the code the same way the car does - by listening to the code, generally at 315 or 433MHz.
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    Quote Originally Posted by MagiMaster View Post
    You only need 36 bits of ID to have about 10 unique numbers for every person on the planet, so if the key can communicate just 36 blips to the locking system it'd be able to do the job. (They probably use more bits than that though.) I don't actually know the details of how the keys transmit those bits though, but I imagine it's something similar to how RFID works. In RFID, the reader supplies the power in the form of a radio wave which the RFID tag echos back in a certain pattern.
    Would this be how the little stick-on pieces attached to merchandise alert an alarm, if the stuff is stolen from a store? How does reading the bar code by the cash register deactivate the device? joc
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    Forum Radioactive Isotope MagiMaster's Avatar
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    I think there are probably several different systems in use and I don't actually know the details of any of them, but I can make an educated guess.

    It's possible that if the store used RFID tags to track products, then they could have the store computers deactivate that product from the security system as it was being checked out. This may or may not be connected to a barcode as some stores take an extra step of running the item across either a strong magnet or some other device. (I don't think a strong magnet would have much effect on an RFID tag though.) I know some book stores do use RFID, but not exactly how.

    Some other stores don't use RFID tags but other security devices that carry no information and must be removed as they're purchased. Some clothing stores use something like ink bombs that would be triggered if you walked out with an unpurchased item. The cashier has a special tool to remove these.
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    Major stores around here anyway, now have weird-looking plastic "caps" affixed to the caps of necked bottles in the liquor departments. The check-out removes them and discards them as they are moved past the her work area. Evidently, they may be reusable, but if not, a lot of plastic is being thrown away for no better purpose than to discourage store theft. One could observe whether she discards them into a "special" catch-bin, or the general trash, from which they would not likely be sought out for re-use, 'ya think? I haven't taken the time to closely inspect one of these things, as I buy no alcoholic stuff. jocular
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    Well, if the store spends less on the extra plastic than they lose to theft, it's a good deal for them at least. Although plastic is recyclable, so even if they're being discarded it may not be completely wasted.
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    Forum Bachelors Degree GoldenRatio's Avatar
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    Quote Originally Posted by jocular View Post
    Major stores around here anyway, now have weird-looking plastic "caps" affixed to the caps of necked bottles in the liquor departments. The check-out removes them and discards them as they are moved past the her work area. Evidently, they may be reusable, but if not, a lot of plastic is being thrown away for no better purpose than to discourage store theft. One could observe whether she discards them into a "special" catch-bin, or the general trash, from which they would not likely be sought out for re-use, 'ya think? I haven't taken the time to closely inspect one of these things, as I buy no alcoholic stuff. jocular
    I have not seen these, However more than likely these are just magnetic locks, much like what they use on t-shirts. a simple magnetic removal and thrown into a special bin to be placed back on the next item or sent out to the factory to be placed back on.

    I doubt they are anything more complicated than that.
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