I know you're looking for a automatic, sensor based system, but I was looking at a pseudo-mega-yacht in Monterey a couple of years ago (oh, 75 footer or so) that was moored on the finger pier adjacent to the launch ramp. After a night dive, I did a brief surveillance run around the thing; noticed that a small compartment at the stern was occupied by a security guard who was monitoring about a dozen small CCTV screens, in addition to checking who was boarding (the stern gate was the only one in use at the time.) He might have had a shotgun. Dunno.
Just thought I'd mention it.