24 volt. Consists of a Rule-A-Matic Plus Float Switch and an in-dash gauge that features both a visual and an audible 85 db alarm. Allows an unmanned compartment to be constantly monitored. For additional compartments add additional Rule Float Switches. Complies with CFR 182.530 which requires a visual and audible alarm in each unmanned space on commercial vessels at least 26′ in length.