Peephole Cam - Doesn't Detect Motion Through Storm Door

Like the subject says my Peephole Cams don't detect motion through my storm doors. The doors have plain ol' clear untinted glass, and no screens in the cams' field of view. I can stand on the porch, wave my arms, jump around, and cause all kinds of commotion - nothing. As soon as I open the storm door all of a sudden the cams can see me and I get notifications. Why is this? What kind of motion detection do these cams use that a pane of clear glass prevents it from working?