A motion sensor includes an infrared detector with a first set of detector elements and a second set of detector elements. The motion sensor also includes an optical system to direct electromagnetic energy from a first row of monitored volumes spaced at a pitch in a first direction onto the first set of detector elements and to direct electromagnetic energy from a second row of monitored volumes spaced at the pitch in the first direction onto the second set of detector elements. The second row of monitored volumes has an offset from the first set of monitored volumes in the first direction and the first row of monitored volumes and second row of monitored volumes are substantially non-overlapping.