Launch alert allows you to determine the correct water line required for launching and loading your boat. The wireless receiver plugs into the tow vehicle power source and gives and audible "Beep" when the sensor contacts the water. The wireless sensor mounts to the inside of the trailer frame with double sided foam tape. Launch alert installs in minutes. No more telling the driver to "pull forward" or "comeback". Launch alert gives you the perfect depth every time you back into the ramp, speeding up the launching and loading process at busy ramps. The compact wireless system includes batteries.