Introducing Bob (create.it)

A scenario is Bob would be deployed in protected ocean areas that are frequently trespassed. Though these areas are protected on paper, the areas are so vast, and the actual guards so few that the protection is non-existent. Bob could sit on the ocean floor listening for boat engines and the like, on detection he can rise to the surface and signal the relevant authorities for help. Once done bobbing, he can descend and go back into power saving/listening mode.