Electro-Magnetic EAS systems create a low frequency electromagnetic field from the pedestal devices. The hard tag material reacts to this magnetic field and causes a signal to be generated back from the tag. The EM system picks up this signal and an alarm is generated.
URL: http://www.tycoemea.com/English/Products/EAS/emsystems.asp
URL: http://www.tycoemea.com/English/Products/EAS/emsystems.asp
