urveillance) A security system for preventing theft in retail stores that uses disposable label tags or reusable hard tags attached to the merchandise. An alarm is triggered when walking through detection pedestals at the store exit if a disposable tag was not deactivated or a reusable tag was not removed at the checkout counter. Also called "single bit RFID tags" because the tag is either on or off, the primary EAS technologies are radio frequency (RF), acousto-magnetic (AM) and electromagnetic (EM).
Radio Frequency (RF)
Looking somewhat like RFID tags, RF EAS tags comprise an inductor (coil) and capacitor in series. The transmitting pedestal sends out an RF signal, which causes the activated tag to resonate, and the phase difference of the signals is detected at the receiving pedestal. RF systems that transmit a range of frequencies to accommodate different labels are called "swept RF." To deactivate disposable RF tags, the tag is waved over a high energy transmitter at the checkout counter that blows a built-in fuse and partially destroys the capacitor. See RFID
AM tags are made of two strips of metal that are magnetized for activation. The transmitter pedestal sends out 58 kHz pulses, which cause the metal to oscillate. The receiving pedestal detects a tag when the transmitter is in between pulses, but a signal is still resonating from the tag. To deactivate disposable AM tags, the tag is demagnetized at the checkout counter.
Widely used in Europe and around the world, EM tags have a metal strip or wire that is demagnetized for activation. A low-frequency alternating current is transmitted from the pedestal, and the tag generates harmonic frequencies that are picked up by the receiver using signal processing. To deactivate disposable EM tags, the tag is magnetized at the checkout counter, exactly the opposite of the AM tags.
The Detection Zone
EAS pedestals pick up activated tags in their detection zone. Signals from the transmitting pedestal are re-radiated by the tag to the receiving pedestal. Although the pedestals serve as a warning, transmitters and receivers can also be hidden in exits. Some systems can use only one pedestal to transmit and receive. (Top image courtesy of Checkpoint Systems, Inc., www.checkpointsystems.com)
Soft and Hard Tags
Disposable RF tags can be concealed within ordinary labels, such as the price label and innocuous shopping cart label in the top image. Reusable hard tags (bottom) must be removed by the clerk at the checkout counter. (Images courtesy of Checkpoint Systems, Inc., www.checkpointsystems.com)