We claim the ornamental design for a motion detecting lightbulb, as shown and described.
FIG. 1 is a top view of one embodiment of a motion detecting lightbulb assembly showing my new design;
FIG. 2 is a right side/front view thereof, the left side/front view and rear view are mirror images of the right side/front view and are therefore not shown;
FIG. 3 is an isometric top view thereof;
FIG. 4 is a bottom view thereof;
FIG. 5 is a top view of another embodiment of a motion detecting lightbulb including a light-emitting diode array and a motion detector;
FIG. 6 is a right side/front view thereof, the left side/front view and rear view are mirror images of the right side/front view and are therefore not shown; and,