Abus opening detectors 2 core 4 core brown 2m 4m 5m abus fu7350b p the abus fu7350b opening detector 2 core brown 2m is a magnetic contact for protecting doors and windows unauthorised opening is detected and reported to the alarm centre the opening detector consists of a magnetic contact reed and a magnet these are fitted parallel in front of or at right angles to each other at a maximum distance of 13mm apart p p the electric circuit of this nc opening detector is normally clos