This is most likely due to the current configurations on your camera.
Let's have a look!
1. Ensure your motion area and/or intrusion areas ONLY cover the areas you are looking to get notifications for.
2. Remove Line Crossing if it is enabled and configured.
For Line Crossing we are looking for objects in the whole image.
If you have two detectors active at the same time on the camera and if for both the same analytic are selected...
IE for this example let's say there is a motion analytic and a line crossing analytic and both are configured to look for people:
...you will be getting alerts for objects outside of the motion perimeter via the line detection analytic.
Rain drops also trigger line crossing. In its turn, line crossing triggers object search according to it's rule set up and because this line crossing search is happening for the whole frame you will receive alerts outside of the frames configured.