An EAS system or electronic article surveillance system works with detection antennas that are installed at the exit of the store and the hard tags or labels attached to the articles sold in the store. The detection antennas constantly emit electromagnetic energy. When a customer passes these antennas with an article, a hard tag or label - if it is not deactivated - causes a short electromagnetic signal that is received by the antennas and results in an alarm.
The hard tags or labels themselves do not contain transmitters but an electric current is generated by the electromagnetic field of the antennas. Electric current is only generated during the short moment that the article is carried past the detection antennas and an electromagnetic interaction occurs between the antenna and the hard tag.
Several electromagnetic frequencies are used for antitheft detection. The EAS systems of the EM type (electromagnetic) and AM type (acousto-magnetic) work with extremely low or intermediate electromagnetic frequencies. The RF type works on radio frequencies.
You probably have seen the EM label (see photo) on a page in a book you borrowed from the library. These labels are reusable.
You often find the AM label (see photo) on clothes. These labels are a bit more expensive and that is why they are mostly attached to more expensive articles.
The RF systems work on radio frequencies. You often see the RF label (see photo) in supermarkets on small articles. 