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How can I make this? Does it exist?

Discussion in 'General Electronics Discussion' started by huskysvg26, Mar 30, 2010.

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  1. huskysvg26

    huskysvg26

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    Mar 30, 2010
    Hi,

    So I am an electronics newbie looking to build a device to help me ensure people are not taking my some of my valuables.

    To give a quick background recently I have found a couple of items missing from my house and I am unsure who might have taken them. I have a few more valuables left that I believe whoever took the ones before might have some interest in taking. Rather than making everyone aware that I know that these items are being stolen I would like to catch the person(s) in the act.

    What I want to build is an electronic device that notifies me when one of my valuables has left a certain range, say 20 feet. I would like to be able to attach a small device (transmitter of some sort) to the valuable (easily hidden, hopefully no bigger than a dime) and then have a retriever that counts how many incoming signals it receives. Basically it would be one receiver with a count and a transmitter on each item.

    If i was to put the transmitters on 5 items I would want the receiver to let me know that all 5 items are still within a certain distance (I would prefer a digital display with the number of items in range). When one of the items is removed I would like it to show me only 4 items are within that distance. This will allow me to know when the item has left my house and go get the person as they are trying to leave with it.

    Being I have no idea what this piece of electronics would be called or even where to begin researching how to make one I am looking for the advice of the forum to get me started.

    Any and all advice / suggestions are welcome. I appreciate you taking the time out to point me in the right direction

    Thanks,

    Newbie
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,839
    Jan 21, 2010
    The solution may cost more than your valuables :)

    One option is to use RFID tags. Their range is generally quite small though. The electronics to read them (especially from a distance) is not going to come cheap.
     
  3. huskysvg26

    huskysvg26

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    Mar 30, 2010
    When you say the range is quite small, how small are we talking?
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,839
    Jan 21, 2010
    Google is your friend.

    This mob reckon 10 metres.
     
  5. huskysvg26

    huskysvg26

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    Mar 30, 2010
    So I did some googling and I have a couple of questions:

    -Would it be possible to have the reciever be battery operated rather than USB or any other power source? Seems like most of what I am seeing is pretty expensive and needs to be attached to a power source. I would prefer the reciever be mobile.

    -Most of the RFID tags I saw seemed to be rather thin, are they bendable? Could I put them around a marker if I wanted without losing the ability for it to track correctly?
     
  6. 55pilot

    55pilot

    434
    3
    Feb 23, 2010
    What kind of devices are you trying to protect? A pair of ear-rings or a big screen TV?

    Where do they go when they are stolen? Do they end up in a sibling's room? Do you know where the thief takes them?

    The answer will be different for each of these situations.

    ---55p
     
  7. huskysvg26

    huskysvg26

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    Mar 30, 2010
    Im thinking more along the lines of video games. I would like to hide the tranmitter in the video game case.

    Typically they are taken out of my house when stolen and I dont know where they take them. This is less to retrieve the items but more to confront the person as they try to take them.
     
  8. 55pilot

    55pilot

    434
    3
    Feb 23, 2010
    As Steve originally suggested, a RFID tag, which is what stores use for theft protection would be perfect for this. But setting up something like this is not going to be cheap or easy. The only time it would work is if you are present when the device is walking out the door.

    So your alarm goes off and you confront the guy. He denies it and is offended that you are accusing him and want to check his bags and his pockets. Have you thought about what you are going to do next? I do not know where you are located, but in most places you do not have the right for forcibly search him, so he is going to get away and you can count on it that he will raise a huge stink about your accusation to every mutual friend and strangers. The police are unlikely to help if you report it after the fact.

    Your best bet may be to better control who has access to your things and the type of people you are choosing to hang around with. If you hang around thieves, it is only a matter of time before you get into trouble yourself.

    ---55p
     
    Last edited: Mar 30, 2010
  9. huskysvg26

    huskysvg26

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    Mar 30, 2010
    I'm more interested in the technology than how it applies to this exact situation. I understand that it would be pricey and their would be issues with confronting the theif but thats less of the issue to me.

    Assuming I choose to make this,and assuming I was present at my house at all times to catch the person, could I make the reciever be battery powered so I could carry it on me? Also, im assuming all the tags are unique meaning that it would be able to relay the count of how many tags are in the specified area?

    Im more probing about how this works, assuming the items being stolen were valuable paintings worth millions I see something like this having value and the costs being acceptable.

    I appreciate all the input people have provided so far, comments are very much appreciated.
     
  10. 55pilot

    55pilot

    434
    3
    Feb 23, 2010
    The way store security works is that the RFID tags are passive devices. They have RFID detectors at the entrances/exits to the store and an alarm goes of when the device gets close enough to the detectors. That is the simplest way to do it, if you have a few exits.

    In your case, if there is only one main door and one back door, you can get away with this. After the first time, the thief would know to pass it out the window and it will get much more involved to install a detector at every window. There are other ways to defeat such a system, but I am not going to discuss those here as someone reading can use the knowledge to shoplift.

    The approach you seem to be focusing on is not RFID. It is a transponder approach where the device checks in with a home base and if the home base does not get a ping it raises an alarm. That is a much more complicated system as each device has to be active, which means a battery. If you are looking for a missing ping, you need to ping frequently enough to detect the missing device soon after it goes missing. Checking every 2 minutes is likely to not be fast enough. The more frequently you ping, the more battery the target device is going to use and the bigger battery it will require. Without designing the system, my gut feeling is that such a system would be unpractical due to the battery size issues.

    There are also remotely powered active RFID tags. They harvest energy from a burst of RF power and use that to actively respond. Unfortunately they are short range enough that it will not be practical to get them to work in this sutuation.

    ---55p
     
  11. hyudryu

    hyudryu

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    Feb 24, 2010
    You know you can use laser sensors and when that signal gets interrupted, it can trigger a camera to see whos doing it. Use IR lasers.
     
  12. neon

    neon

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    Oct 21, 2006
    take my advice lock doors spy games only works for honest people a person that want to rip you off all of the gadgets will not help. And to make it more plain if you install a trap then the bad guy can sue you for damages caused by you .
     
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