FIG. 1 is a front perspective view of a motion sensor of the present invention; FIG. 2 is a front view thereof; FIG. 3 is a first side view thereof; FIG. 4 is a second side view thereof; FIG. 5 is a top view thereof; FIG. 6 is a bottom view thereof; and, FIG. 7 is a rear view thereof. The broken lines shown represent unclaimed subject matter and form no part of the claimed design.