Abstract: A fuel filler alarm for boats includes a housing, a whistle element on the housing and a suction ring on the housing. The suction ring is operable for detachably securing the housing to the hull of a boat adjacent a fuel tank vent thereon so that air passing outwardly through the vent passes through the housing and the whistle element. The whistle element is responsive to the outward flow of air through the fuel tank vent during a fuel filling operation for producing an audible whistling sound, while sound essentially stops when the associated fuel tank reaches a substantially full condition.