Hacking apart Sensor Tag from Clothes

Well, I have still in no way started the Electronics work again “yet”.  But there are things really fascinating to wrest your focus.
Last week I bought up this T-shirt from U.S. Polo Assn. (Karol Bagh, Delhi).  Its one of my habit that once I purchase a T-shirt from a shop and if I really like it on trying I do not pull it off, rather I make the payment and come home or do further shop*ing continuing wearing it.
It has been a cliche for me to get the alarm triggered at the gate many a times at Shops because since I don’t wear off the t-shirt and thus its EAS(Electronics Article Surveillance) tag makes the noise as if I am committing larceny.

As I read my way through on internet, I got to know that there are a lot of people who sometimes get their clothes shipped with Tag still remaining on it. Sometimes it happens like my case. Sometimes people shoplift too, whatever be the case, believe me you are not surely going to like it wearing a T-shirt or other cloth with a tag on it.
Special case when you travel by Metro, even the gurads tends to say, “this one appears to be a shoplifted product”


But this time, when I purchased this T-shirt, I didn’t get the tag removed and came off the shop  easily without getting the Alarm triggered.  I guess the Machine i.e. The transmitter or Receiver or the MonoMachine there at the U.S. Polo (karol Bagh Center) was not working…well there is an opportunity for many to shoplift there, which is surely not a good thing.

When I came back home, I called them up and they said to bring the T-shirt back to them in order to get it removed.  Well, being a big lazy ass, that was not an option for me.  So I tried removing it apart.
Here is the video I made for it.


pulling  apart the sensor

The Techy part:

Well, It appears the coil is energized by a nearby magnetic field, not necessarily a magnet–but a field of some sort. It induces a current in the coil, a magnetic field which resonates at some particular frequency which is sensed by the gates somehow and thus triggering the alarm.  I knew it always, Basic Physics has always been a BITCH!

What is an EAS System?

Electronic Article Surveillance (EAS) is a technological method for preventing shoplifting. It usually involves three components:

  • Electronic Antenna
  • Deactivator or Detacher
  • Electronic Tag

Special tags and labels are fixed to merchandise or books. These tags or labels are removed or “deactivated” by the clerks when the item is properly bought or checked out.

Labels are deactived using a “Label Deactivator”.

While ringing up purchases a cashier should pass each product label across the “Deactivation Pad”.

To remove a Hard Tag a cashier uses a “Detacher” which releases the pin.

After a label is deactivated or a tag is removed the customer can then pass by the antenna without any alarm.

At the exits of the store, a detection system sounds an alarm or otherwise alerts the staff when it senses active tags are passing by.

Types of EAS systems and how they work.

There are several major types of electronic article surveillance systems :

So, Our system appears to be a kind of Radio Frequency, I am guessing it from the Capacitor and the coil.

As wiki and other sources say,Radio-frequency systems

These tags are essentially an LC tank circuit. An LC circuit is a resonant circuit or tuned circuit that consists of an inductor, represented by the letter L, and a capacitor, represented by the letter C that has a resonance.
At these frequencies, even small periodic driving forces can produce large amplitude vibrations, because the system peak anywhere from 1.75 MHz to 9.5 MHz. The most popular frequency is 8.2 MHz. Sensing is achieved by sweeping around the resonant frequency and detecting the dip. Deactivation for 8.2 MHz label tags is achieved by detuning the circuit by partially destroying the capacitor.

anti-theftA label — basically a miniature, disposable electronic circuit and antenna — attached to a product responds to a specific frequency emitted by a transmitter antenna (usually one pedestal of the entry/exit gate). The response from the label is then picked up by an adjacent receiver antenna (the other pedestal). This processes the label response signal and will trigger an alarm when it matches specific criteria. The distance between the two gates, or pedestals, can be up to 80 inches wide. Operating frequencies for RF systems generally range from 2 to 10 MHz (millions of cycles per second); this has become standard in many countries. Most of the time, RF systems use a frequency sweep technique in order to deal with different label frequencies.


A really descriptive video is this one,