All electronic article surveillance systems emit electromagnetic energy and thus can interfere with electronics.
Magneto-harmonic systems need to bring the tags to magnetic saturation and thus create magnetic fields important enough to be felt through a small magnet. They routinely interfere with CRT displays. Demagnetization/remagnetization units also create intense fields.
Acousto-magnetic systems use less power but their signals are pulsed in the 100 Hz range.
Radio-frequency systems tend to be the least interfering because of their lower power and operating frequency in the MHz range, which makes it easy to shield against.
A March 2007 study by the Mayo Clinic in Rochester, Minnesota reported instances where magnetic or acousto-magnetic EAS systems located at the front of retail stores caused a pacemaker to fail and a defibrillator to trigger, shocking the persons they were implanted in.[4]
There are also concerns where some installations are on purposely done to exceed the rated specifications of the manufacturer which exceed all tested and certified magnetic fields.