Seen a movie or tv show about 20 years ago with these. They were shooting 9mm or 223 rounds. They looked just like an electrical box, so very undetected unless it fired a shot. In the show, it was automated by movement or manually fired. I think they were also suppressed because when a shot was fired, the cops couldn't figure out where the shots came from until a detective put 2 n 2 together and noticed the boxes didn't belong in the areas of the buildings.