An alcohol detector for detecting high concentrations of alcohol in a fuel tank and for providing evidence that the alcohol was present even after it has been removed. In one aspect, the alcohol detector includes a cathode and an anode of different materials and spaced from one another. The anode experiences galvanic corrosion at a faster rate when exposed to high concentrations of alcohol than it does when exposed to unleaded gasoline. Thus, the amount of corrosion present on the anode provides evidence of the past presence of an improper fuel in the fuel tank. In another aspect, the alcohol detector is a dye printed on a fuel pump. The dye visually changes color intensity in the presence of high concentrations of alcohol to provide evidence of the past presence of alcohol.