A motion detector with anti-mask monitoring recognizes if the detector’s detection range is accidentally or intentionally concealed, e.g. by furniture, curtains or other large objects, within a radius of 0.5 m after the calibration procedure. The detector displays a fault in this case.
The anti-mask monitoring function is integrated only in motion detectors of VdS class C. You can find further information here:
Product Manual (see chapters 2.6 and 2.7, which describe the motion detectors).