The ornamental design for a monitoringdevice, as shown and described.
FIG. 1 is a perspective view showing the new design for a monitoring device;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The portions of the monitoring device in FIGS. 1, 3-5, and 7 shown in broken lines are included to show features that form no part of the claimed design.