Electronic article surveillance

Electronic article surveillance (EAS) is a technological method for preventing shoplifting from retail stores, pilferage of books from libraries or removal of properties from office buildings. Special tags are fixed to merchandise or books. These tags are removed or deactivated by the clerks when the item is properly bought or checked out. At the exits of the store, a detection system sounds an alarm or otherwise alerts the staff when it senses active tags. Some stores also have detection systems at the entrance to the restrooms that sound an alarm if someone tries to take unpaid merchandise with them into the restroom. For high-value goods that are to be manipulated by the patrons, wired alarm clips called spider wrap may be used instead of tags.

Surveillance tags that could be attached to items in stores were first invented by Arthur Minasy in 1966.

There are several major types of electronic article surveillance systems:

These tags are made of a strip of amorphous metal (metglas) which has a very low magnetic saturation value. Except for permanent tags, this strip is also lined with a strip of ferromagnetic material with a moderate coercive field (magnetic "hardness"). Detection is achieved by sensing harmonics and sum or difference signals generated by the non-linear magnetic response of the material under a mixture of low-frequency (in the 10 Hz to 1000 Hz range) magnetic fields.

When the ferromagnetic material is magnetized, it biases the amorphous metal strip into saturation, where it no longer produces harmonics. Deactivation of these tags is therefore done with magnetization. Activation requires demagnetization.

This system is suitable for items in libraries since the tags can be deactivated when items are borrowed and re-activated upon return. It is also suitable for merchandise in retail stores, due to the small size and very low cost of the tags (Tattle-Tape).

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Wikipedia