EAS systems operate from a simple principle regardless of the
manufacturer or the specific type of technology used: a transmitter
sends a signal at defined frequencies to a receiver. This creates a
surveillance area, usually at a checkout aisle or an exit in the case of
retail stores. Upon entering the area, a tag or label with special
characteristics creates a disturbance, which is detected by the
receiver. The exact means by which the tag or label disrupts the signal
is a distinctive part of different EAS systems. For example, tags or
labels may alter the signal by using a simple semi-conductor junction
(the basic building block of an integrated circuit), a tuned circuit
composed of an inductor and capacitor, soft magnetic strips or wires, or
vibrating resonators.
By design the disturbed signal created by the tag and detected by
the receiver is distinctive and not likely to be created by natural
circumstances. The tag is the key element, for it must create a unique
signal to avoid false alarms. The disturbance in the electronic
environment caused by a tag or label creates an alarm condition that
usually indicate someone is shoplifting or removing a protected item
from the area.
The nature of the technology dictates how wide the exit/entrance
aisle may be. Systems are available that cover from a narrow aisle up to
a wide mall store opening. Similarly, the type of technology affects
the ease of shielding (blocking or detuning the signal), the visibility
and size of the tag, the rate of false alarms, the percentage of
detection rate (pick rate), and cost.
The physics of a particular EAS tag and resultant EAS technology
determines which frequency range is used to create the surveillance
area. EAS systems range from very low frequencies through the radio
frequency range. Similarly, these different frequencies play a key role
in establishing the features that affect operation.