This is Underground's marine-rated Bluetooth control knob that offers an easy way to connect wirelessly to your smart phone or tablet. This control knob offers the ability to adjust you smartphone or tablet's volume up and down, play and pause your music, track forward and track backward. Pairing is quick, making Bluetooth control and pairing easy. You can also switch between one additional source (i.e sirius radio receiver or any other smartphone or tablet. Installation is as simple as drilling a single hole in the location pictured.