Passive infrared motion detector comprising a cover part, a base part, a mirror arrangement having active surfaces (5.1), a rectangular lens arrangement and a printed circuit board, the base part accommodating the printed circuit board, on which four passive IR sensors, an IR receiver (7.1) for registering IR remote control signals, a brightness sensor (7.3) for registering ambient brightness and further electronic components are arranged, the mirror arrangement and the rectangular lens arrangement, the base part being covered by the cover part, with - four spherical cap-shaped lenses (3.1) each having a plurality of lens segments (3.1.1) for motion detection or four spherical cap- and truncated coneshaped lenses (3.1) each having a plurality of lens segments (3.1.1) for motion detection being arranged in the corner regions of the rectangular lens arrangement, - the mirror arrangement arranged below the lens arrangement being provided to increase the optical resolution of the lens arrangement, - the active surfaces (5.1) of the mirror arrangement and the passive IR sensors assigned to these in each case being arranged with respect to one another such that the active surfaces (5.1) of the mirror arrangement supply mirror images of the assigned passive IR sensors, and the active surfaces (5.1) of the mirror arrangement being provided with a reflective coating, - the cover part located above the lens arrangement having a centrally arranged plastic web (1.1) with at least two openings (1.3), into which transparent cap parts are incorporated, and - light channels (5.2, 5.3) for accommodating light guides being arranged under the cap parts, the said light guides interacting with the IR receiver (7.1) and brightness sensor (7.3) located underneath, - the registration of ambient brightness and IR remote control signals being implemented through the plastic web (1.1), which to this end interacts with the relevant light channels (5.2, 5.3). - four spherical cap-shaped lenses (3.1) each having a plurality of lens segments (3.1.1) for motion detection or four spherical cap- and truncated coneshaped lenses (3.1) each having a plurality of lens segments (3.1.1) for motion detection being arranged in the corner regions of the rectangular lens arrangement, - the mirror arrangement arranged below the lens arrangement being provided to increase the optical resolution of the lens arrangement, - the active surfaces (5.1) of the mirror arrangement and the passive IR sensors assigned to these in each case being arranged with respect to one another such that the active surfaces (5.1) of the mirror arrangement supply mirror images of the assigned passive IR sensors, and the active surfaces (5.1) of the mirror arrangement being provided with a reflective coating, - the cover part located above the lens arrangement having a centrally arranged plastic web (1.1) with at least two openings (1.3), into which transparent cap parts are incorporated, and - light channels (5.2, 5.3) for accommodating light guides being arranged under the cap parts, the said light guides interacting with the IR receiver (7.1) and brightness sensor (7.3) located underneath, - the registration of ambient brightness and IR remote control signals being implemented through the plastic web (1.1), which to this end interacts with the relevant light channels (5.2, 5.3).