There's a lot of methods retailers use for loss prevention. A very popular method is to use a system that attaches special tags onto everything so that an alarm goes off whenever a shoplifter tries to walk out with an item.

These tag-and-alarm systems, better known as electronic article surveillance (EAS) systems, identify articles as they pass through a gated area in a store. This identification is used to alert someone that unauthorized removal of items is being attempted. Using an EAS system enables the retailer to display popular items on the floor, where they can be seen, rather than putting them in locked cases or behind the counter.

The type of EAS system dictates how wide the exit/entrance aisle may be, and the physics of a particular EAS tag and technology determines which frequency range is used to create a surveillance area. EAS systems range from very low frequencies through the radio frequency range (see How Radio Scanners Work). These EAS systems operate on different principles, are not compatible and have specific benefits and disadvantages.

Three types of EAS systems dominate the retail industry:

  • Radio Frequency (RF) Systems are the most widely used systems in the United States today and RF tags and labels are getting smaller all the time. A label that contains a miniature, disposable electronic circuit and antenna is attached to a product. The label 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.

    The RF circuit inside a label looks like this.

  • The Electromagnetic (EM) system, which is dominant in Europe, is used by many retail chain stores, supermarkets and libraries around the world. In this technology, a magnetic, iron-containing strip with an adhesive layer is attached to the merchandise. This strip is not removed at checkout -- it's simply deactivated by a scanner that uses a specific highly intense magnetic field. One of the advantages of the EM strip is that it can be reactivated and used at a low cost. What most people refer to as an electromagnetic tag is actually a metal wire or ribbon that has high permeability, making it easy for magnetic signals to flow through it. A magnetized piece of semi-hard magnetic material (basically, a weak magnet) is put up next to the active material to deactivate it. When you magnetize the semi-hard material, it saturates the tag and puts it in its inactive saturated state.

    The EM system works by applying intensive low frequency magnetic fields generated by the transmitter antenna. When the strip passes through the gate, it will transmit a unique frequency pattern. This pattern is, in turn, being picked up by an adjacent receiver antenna. The small signal is processed and will trigger the alarm when the specific pattern is recognized. Because of the weak response of the strip, the low frequency (typically between 70 Hz and 1 kHz) and intensive field required by the EM system, EM antennas are larger than those used by most other EAS systems. The maximum distance between entry pedestals is 40 inches. Also, because of the low frequency here, the strips can be directly attached to metal surfaces. That's why EM systems are popular with hardware, book and record stores. (Check out the patent for more details!)

    Magnet-based systems have a small wire or metal strip hidden in the tag.

  • Another magnetic technology is the acousto-magnetic system, which has the ability to protect wide exits and allows for high-speed label application. It uses a transmitter to create a surveillance area where tags and labels are detected. The transmitter sends a radio frequency signal (of about 58 kHz) in pulses, which energize a tag in the surveillance zone. When the pulse ends, the tag responds, emitting a single frequency signal like a tuning fork. While the transmitter is off between pulses, the tag signal is detected by a receiver. A microcomputer checks the tag signal detected by the receiver to ensure it is at the right frequency, is time-synchronized to the transmitter, and that it is at the proper level and the correct repetition rate. If all these criteria are met, the alarm occurs.
In each case, an EAS tag or label is attached to an item. The tag is then deactivated, or taken from an active state where it will alarm an EAS system to an inactive state where it will not flag the alarm. The disposable tag is deactivated by swiping it over a pad or with a handheld scanner that "tells" the tag it's been authorized to leave the store. If the item has not been deactivated or detached by the clerk, when it is carried through the gates, an alarm will sound.

The use of EAS systems does not completely eliminate shoplifting. However, experts say, theft can be reduced by 60 percent or more when a reliable system is used. Be sure to read How Anti-Shoplifting Devices Work for more in-depth information on this subject.

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