At extreme ocean depths where no light from the surface penetrates, how can divers find their way around? By using the same techniques as sea creatures. don’t think that there is anything as sophisticated as this device in a handheld form. Present-day divers can equip themselves with simple handheld sonar devices that look like flashlights. They are used to make a simple depth-check possible from the surface (from a kayak or canoe) or when underwater. These devices are simple, however; you point them at the bottom and press the button and a single result is provided.