As the name implies, SonarPhone turns your smartphone or tablet into a fully functional touch screen sonar system that will rival the performance of sonar systems costing hundreds more. You dont need cell phone coverage to use it, the SonarPhone Sonar Transmitter will work anywhere in the world. The SonarPhone transmitter creates its own WiFi hotspot and you can share its signal with as many people as you wish or password protect it just for yourself. To use the SonarPhone App in anything other than "Demo Mode" you will need to connect to an existing SonarPhone Sonar WiFi Transmitter or purchase one of the three options yourself. The T-POD (SP100) is a ultra portable WiFi transmitter systems that has a self contained battery and can be pulled behind your boat, cast or thrown from shore. The T-BOX (SP200) is a more permanently mounted system that is mounted in a boat with access to a 12 volt power supply (not included). Or the T-BOX (SP300) which is the T-BOX mounted on its own 12 volt