The other day, when my friend and I were walking past a departmental shop, a DVD we had with us triggered the shop’s anti-shoplifting system. The security guard came over and helped us figure out that the trigger belonged to a plastic strip attached to the DVD casing which looked like this:
Of course, ordinarily, removing it and throwing it away would be what most people would have done. But, I’m not quite the ordinary person =p
Curious about why such a small strip of metal could prevent theft and transmit signals to trigger an alarm, I decided to take it apart.
It was rather disappointing to see that besides housing a few strips of metal, there really wasn’t any circuits or wires jutting out of that thing. So how does it work?
Here’s a summary of what this site says:
Basically, the strip has a magnetic, iron-containing wire or ribbon inside that has a high permeability that makes it easy for magnetic signal to flow through it. To deactivate this ribbon, you simply use a weak magnet to saturate the tag and this puts it in an inactive saturated state. The active state is the state at which the strip will trigger the alarm.
How does the system work?
At the gate of the shop, there is an intensive low frequency magnetic field generated by the transmitter antenna (those ‘gate’-like things you see near the door). When the active strip passes through, it transmit a unique frequency pattern which is picked up by an adjacent receiver antenna. The signal is processed and if it is recognised, an alarm will be triggered!
Because of it’s low frequency, it can be placed on other metal objects and these metal objects will not trigger the alarm because their permeability is just not high enough.
p.s. sorry if this trivia contained too much scientific terms… If anyone needs a layman explanation, you could drop me a comment and i’ll try to work on a layman explanation. =)
24 comments
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July 7, 2009 at 9:01 am
John
Very insightful! I took one of these apart myself this evening and I was like yourself, disapointed with my findings. I figured the strips were very weak magnets of some kind, but that was all I could surmise. Googled ‘Security Strip Dvd’ and found your write up.
But there’s one thing I don’t get. You’re in the store, you take a DVD of the shelf, walk to the door, through the security ‘gates’ and the alarm is tripped.
Take the same DVD to the till, they scan the barcode, you pay for it, they give the DVD case back to you, but yet this time, you can walk through the ‘gates’ without triggering a response and yet, the security strip has not been remains stuck to the DVD case.
I’ve watched the staff handle the DVD case and scan it’s barcode then hand it back to you. As far as I am aware, they don’t tamper with it or change its frequency, so I’m wondering how the strips are deactivated?
April 17, 2016 at 6:51 am
Nate
They have a magnet inside the scanner that deactivates it. If not done properly you will still beep walking out.
July 8, 2009 at 7:34 am
xae
Hi!
Next time go check if there’s some kind of platform on the table. I think they actually use electromagnets to deactivate the strips so that it does not trigger the alarm. I noticed most places have just a simple black or blue pad that is slightly raised from the table. That’s where you can deactivate the strips. You shouldn’t put any magnetic materials on that as well in case it gets deactivated. Hence, things like credit cards should definitely not be placed there. =)
August 14, 2009 at 12:48 am
Christopher
Thanks, was also just trying to figure out how these things worked after also taking it apart and being dissapointed at only finding three strips of foil.
What I was wondering though is… A couple days ago I purchased some items from a store with these devices on. They were imobalised in that store, and obviously didn’t set anything off when leaving.
Yet I then found one item was faulty, and returned it to a seperate (chain) store. And in this store, same item, same anti-theft sticker thing (seemingly imobalised in first store), yet it set off their alarms. How would that happen then? I deffinately didn’t have anything else on me other than the stuff I’d walked out of the first store with that didn’t set anything off.
August 14, 2009 at 12:51 am
Mid-Week Muppets « inaudible Games
[…] back anyways. They’ll curse the day they sold it too me, I’m sure. Oh, here’s an explanation of the foil […]
August 14, 2009 at 6:27 am
xae
Oh hey that’s interesting! So this item was inactivated but somehow still managed to trigger the alarm? It’s like how some library books can also activate alarms in shops. Wonder how that works.
September 22, 2009 at 3:47 pm
sburner
Hey. I took one of these apart just a few minutes ago and then googled it. Found your post, etc etc 🙂
Just to comment: they deactivate it by gently rubbing the dvd or this strip on the counter. There is a magnet under the countertop. If you look closely, the countertop is probably warn out where the magnet is located.
Just my 2cents.
December 12, 2009 at 6:50 pm
Adam
How strong of a magnet is required to deactivate the strips;and in what manner should it be used.
April 7, 2011 at 8:24 am
zack
what are those strips of metal made of?????
May 14, 2012 at 7:34 pm
sparky lol
i just read on this other site that you need a strong magnet and if you have an old computer lying around you can get the neodymium magnet out, i youtubed it and you can find tons of vids teaching you how to get one out or you can buy one on ebay .. damn we;re bad!
November 22, 2012 at 12:28 pm
matt
so how do you saturated the strip? also..whats about the strips that are buried and hidden inside a box? last, are they making strips now that the magnet willl not work on?
March 28, 2013 at 9:36 am
logan patch
Me and a friend have a bet going on, i belivethe strips are magnizium.does anyone have any ideas?
August 5, 2013 at 9:30 pm
intelligent cruiser book
Hey there! It seems as though we both have a interest
for the same thing. Your blog, “Anti-theft strips | stuff.” and mine are very similar.
Have you ever considered authoring a guest write-up for a related
website? It is sure to help gain publicity to your blog (my site recieves a
lot of targeted traffic). If you happen to be interested, e-mail me at:
vaughnbarbee@warpmail.net. Many thanks
July 9, 2014 at 11:33 am
doug
This is crazy..so pretty much a magnet off a speaker will,or can deactivate a alarm strip on a item in a merchant store….
January 2, 2015 at 11:07 am
rob
the neodymium magnets u get out of a computer drives can and most definately wil deactivate the strips. Also the magnets will open all security boxes and the s3 alpha spider wires!!!!!
January 21, 2016 at 3:07 am
Sapphire christian
Where do you put the magnet to deactivate the strip and where do I purchase one of these magnets
October 30, 2015 at 11:41 am
Alexa
So if I got a little block of a neodymium magnet, where do I need to put it to deactivate a sensor on a DVD or Video Game? Are they located right under the barcode?
December 13, 2015 at 11:40 am
Dan
Very interesting comments. I cut one open and found the metal strip.
I cut the strip in half. Are these strips dangerous to handle?
January 21, 2016 at 3:05 am
Sapphire christian
What kind of magnet and where do I purchase such magnet
April 10, 2017 at 6:14 am
Seth Renville
I would like tho opposite, a more scientific explanation, about whether a neodymium magnet, or a series of them, would be too steong, and cause the magnetic strip to set off the sensor.
May 17, 2017 at 9:00 am
Rhonda
THANKS that already explained what I thought..
June 5, 2017 at 2:53 am
Kai
Where do you put the magnet to deactivate the magnetic sensor?
November 18, 2017 at 1:43 am
Kenneth J King
Will rare earth magnets deactivate these strips?
November 30, 2017 at 6:22 am
Norma Barrera
So if I run a strong magnet on the strip will it deactivate