This document describes how the Checkpoint resonant tag system may work (record and clothing stores). The following data is provided for informational purposes only, and no guarantee is made to the accuracy of the contained information.
These systems appear to rely on a resonant tank circuit that is responsive to signals from about 8500-9100 khz. The signal appears to be swept between these two values (at least from the point of being received on a shortwave radio). The change in the signal profile generated by a high Q tank circuit is what sets this type of alarm system off. Resonant tanks built for these frequencies will set of checkpoint alarm systems.
Tags have no active components, disposables can be deactivated electronically in a manner that is not injurious to magnetic products.
Very easy to defeat tags, some falsing problems due to other items being resonant in the detection band. Coils must be close together and can interfere with store exit layout.