A motion-activated decorative lighting fixture with a PIR motion detector hidden behind a decorative slotted wall of the fixture body. The motion-activated decorative lighting fixture includes a motion detector housing that forms an integral part of the lighting fixture body. The housing includes a slotted vertically extending exterior wall around the housing with an array of elongate vertically extending slots horizontally spaced apart from one another and extending along at least a portion of the wall. One or more PIR sensors are disposed within the housing, and a segmented Fresnel lens array is disposed within the housing behind the slots to direct infra-red energy from a monitored field of view to a sensor. The lens array includes a plurality of columns of lenslets, at least a portion of which have at least two lenslets disposed one above the other. Each column is aligned with a corresponding slot so as to direct infra-red energy from a monitored zone passing through the corresponding slot to a sensor. The configuration defines an optical path for infra-red energy emanating from a detection zone in the field of view, the optical path passing through a given slot and a lenslet aligned with the slot and on to a PIR sensor.