The ornamental design for a petactivitymonitor, as shown and described.
FIG. 1 is a perspective view of a pet activity monitor showing the new design;
FIG. 2 is a front view of the pet activity monitor of FIG. 1;
FIG. 3 is a back view of the pet activity monitor of FIG. 1;
FIG. 4 is a left view of the pet activity monitor of FIG. 1;
FIG. 5 is a right view of the pet activity monitor of FIG. 1;
FIG. 6 is a top view of the pet activity monitor of FIG. 1;
FIG. 7 is a bottom view of the pet activity monitor of FIG. 1; and,
FIG. 8 is a side elevational view of the pet activity monitor of FIG. 1, which is connected with a collar and worn on a pet's neck.
The broken line showing of the collar in FIG. 8 is for environmental purposes only and forms no part of the claimed design. Various colors may be displayed on an upper display according to exercise time of the pet.