Occasional vs. informed shoplifters
EAS systems provide a good deterrent against casual theft. The occasional shoplifter, not being familiar with these systems and their mode of operation, will either get caught by them, or will refrain from stealing. Informed shoplifters with appropriate tools can in some cases remove or deactivate tags. However they may miss some tags or may be unable to remove or deactivate all of them, especially if concealed or embedded tags are used. (As a service to retailers, some manufacturers embed security tags in the packaging of their products, or even inside the product itself.) Ink-releasing tags known as benefit denial tags may reduce the rate of successful tag removal. Also, deactivating or detaching tags may be spotted by the shop staff. Shoplifting tools are illegal in many jurisdictions, and can, in any case, serve as evidence against the perpetrators. Hence, informed shoplifters, although they decrease their risk of being caught by the EAS, expose themselves to much greater judicial risks if they get caught with tools or while trying to remove tags, as this characterizes intent to steal.
The possession of shoplifting tools e.g. wire-cutters to cut bottle tags can lead to the suspect being arrested for theft and “coming equipped to steal” within the UK judicial system.
In summary, while even the least expensive EAS systems will catch most occasional shoplifters, traditional surveillance measures are still required against informed ones.
[edit] Installation costs
A single EAS detector, suitable for a small shop, usually costs several thousand dollars or euros. Disposable tags cost a matter of cents. More sophisticated systems, which are more difficult to circumvent, are available, for which the tags are more expensive due to the use of more sophisticated locks. Unlike dummy surveillance cameras, dummy EAS systems are ineffective. As all EAS systems get occasionally tripped, not because of shoplifting, but because of tag deactivation faults, or simply by mindless customers, such dummy EAS systems would be spotted rather quickly. Furthermore, the electromagnetic field of all EAS systems can be easily detected using very simple electronics or with common devices such as radio receivers, or depending on the EAS technology used, portable cassette players.
[edit] False alarms
A major concern with these systems is when false alarms occur. A false alarm (or false positive) is when the alarms go off when a person passes through the gate without having stolen any merchandise. This most often is due to tags on merchandise not being properly deactivated. False alarms are embarrassing not only for honest customers who accidentally set off an alarm, but for the business as well - who now have an upset customer on their hands.
In some older systems electronic devices have been known to set off alarms. RF systems can react even to a coil of wires (for example, a Cat5 cable carried by a forgetful network technician) because stray capacitance forms a LC circuit within the coil itself. It is also possible for alarms to go off without anyone crossing the gates. Such interference is often due to other nearby alarm systems.
[edit] Tag orientation
Except for microwave, the detection rate for all these tags depends on their orientation relative to the detection loops. For a pair of planar loops forming a Helmholtz coil, magnetic field lines will be approximately parallel in their center. Orienting the tag so that no magnetic flux from the coils crosses them will prevent detection, as the tag won’t be coupled to the coils. This shortcoming, documented in the first EAS patents, can be solved by using multiple coils or by placing them in another arrangement such as a figure-of-eight. Sensitivity will still be orientation-dependent but detection will be possible at all orientations.
[edit] Detaching
A detacher is used to remove re-usable hard tags. The type of detacher used will depend on the type of tag. There is a variety of detachers available with the majority using powerful magnets. any store that uses an anti-shoplifting system and has a detacher should take care to have it secured so it can not be removed. Some detachers actually have a security tag inside them, to alert store personnel of them being removed from (or being brought into) the store.
[edit] Magnetic activation and deactivation
Deactivation of magnetic tags is achieved by straightforward magnetization using a strong magnet. Magneto-acoustic tags require demagnetization. However sticking a powerful magnet on them will bias disposable magnetic tags and prevent resonance in magneto-acoustic tags. Similarly sticking a piece of metal, such as a large coin on a disposable radio-frequency tag will shield it. Non-disposable tags will require stronger magnets or pieces of metal to disable or shield since the strips are inside the casing and thus further away.
[edit] Shielding
most systems can be circumvented by placing the tagged goods in a bag lined with aluminum foil. The bag will act as a Faraday cage, isolating the tag from the antennas. Although some vendors claim that their acousto-magnetic systems cannot be defeated by bags shielded with aluminum foil[1], sufficient amount of shielding, on the order of a 30 layers of standard 20µm foil, will defeat all standard systems [2].
Although the amount of shielding required depends on the system, its sensitivity, the distance and orientation of the tags with relative to its antennas, total enclosure of tags is not strictly necessary. Indeed, some shoplifters use clothes lined with aluminum foil. Low-frequency magnetic systems will require more shielding than radio-frequency systems due to their use of [near-field] magnetic coupling. Magnetic shielding, for instance with steel or mu-metal, would be more effective, but also cumbersome and expensive.
The shielding technique is well-known amongst shoplifters and store owners. Some states have specific laws against it.[citation needed]
To deter the use of booster bags, some stores have add-on metal detector systems which sense metallic surfaces.
[edit] Jamming
Like most systems that rely on transmission of electromagnetic signals through a hostile medium, EAS sensors can be rendered inoperative by jamming. As the signals from tags are very low-power (their cross-section is small, and the exits are wide), jamming requires little power. Evidently, shoplifters will not feel the need to follow radio transmission regulations, hence crude, easy-to-build transmitters will be adequate for them. An amateur can therefore design and build a jammer for magnetic, magneto-acoustic or radio-frequency systems without special equipment. For instance, a square wave near 58 kHz driving a coil with less than a watt of power will jam magneto-acoustic systems. As for 8.2 MHz radio-frequency systems, since they are sweeping their frequency, building a jammer for them does not require a precise transmission frequency and therefore neither does it require expensive frequency counting equipment, However, due to their high frequency of operation, building a jammer can be difficult for microwave circuits; these systems are therefore less likely to be jammed. Although jamming is easy to perform, it is also easy to detect. A simple firmware upgrade should be adequate for modern DSP-based EAS systems to detect jamming. However, these systems can usually be circumvented by simpler means (shielding, detaching or deactivation). Hence, the incentive for building jammers is low.
Jamming countermeasures have been implemented by ADT/Sensormatic in their recent AM systems.