Also functions as a dual station intercomFeatures connections for forward and aft PA horns with listen-back and includes bells and whistles for four fog signals. Large backlit keypad and oversized knobs for easy operation even while wearing gloves. Dual-station intercom allows you to connect up to 2 optional MLS-300i speakers with "push to alert" button. When pushed it produces an alert to the station being called. Manufacturer rated waterproof to JIS 7 and submersible to 3' for 30 minutes