Within the retail industry, the devices are generally known as security tags or Electronic Article Surveillance (EAS) tags. The technology favored for modern tags involves a set of gates that transmits pulses of a low-range radio frequency. Inside each security tag is a resonator, a device that picks up the transmitted signal and repeats it.

 

The set of gates also contains a receiver that is programmed to recognize whether it is detecting the target signal during the time gaps between the pulses being broadcast by the gates. Sensing a signal during these intervals indicates the presence of a signal being resonated (rebroadcast) by a security tag in the detection zone.

 

When this occurs, the gates sound an alarm; in some systems, the alarm sound is accompanied by a flashing light.

 

 

 

Radio-frequency identification (RFID) is the use of a wireless non-contact system that uses radio-frequency electromagnetic fields to transfer data from a tag attached to an object, for the purposes of automatic identification and tracking.