Odds are you take your phone with you fishing — despite the possibility of it getting wet — so you might as well make it useful. The Deeper Fishfinder is a small, Bluetooth-powered smart sonar that works with your phone to help you get the most out of every trip. Simply attach it to a fishing line and cast it out to where you plan to fish. As soon as it hits the water, it will start sending back data to the companion app, letting you see the depth, number and location of the fish, water temperature, and more. And thanks to its small size, it can be used in places most fishfinders can't, like from a kayak, shore, or dock.