This term came up during this guide, but you still may not be 100 percent sure what it means. For science gurus, you should know that a transducer is a device that converts energy from one form to another, typically being a signal of some kind. For a fish finder, this is the heart of the entire system. What this device will do is change the electrical pulses into sound waves. In turn, it sends out these sound waves and receives the echoes that it hears. This is what allows you to view what is lurking under the surface. When the transducer sends out these sound waves, you can then see the fish and objects on your GPS device. If you plan to use a marine GPS device as a fish finder, then this is an essential key to the puzzle.