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 set 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 set of monitored volumes spaced at the pitch in the first direction onto the second set of detector elements. The second set of monitored volumes have an offset from the first set of monitored volumes in the first direction.