Activity monitoring device

The design is the visual features of the ACTIVITY MONITORING DEVICE shown in solid lines in the drawings, whether those features are of shape, configuration, ornament, or pattern, or are a combination of any of these features. The portions of the article shown in stippled lines do not form part of the design.Drawings of the design are included.Fig. 1 is a top perspective view of the activity monitoring device;Fig. 2 is a bottom perspective view thereof;Fig. 3 is a top view thereof;Fig. 4 is a bottom view thereof;Fig. 5 is a right side view thereof;Fig. 6 is a left side view thereof;Fig. 7 is a back view thereof; andFig. 8 is a front view thereof.