When your boat is plugged into shore power, stray current corrosion—caused by badly insulated shore power supplies and defective wiring on other peoples boats—can rapidly destroy your anodes and do costly damage to your boats underwater metals. Enter GalvanAlert—the worlds only shore power corrosion detector with reverse polarity indicator. GalvanAlert easily attaches to your 30A shore power inlet and cord set to constantly monitor if there is unsafe corrosion activity or a reverse polarity situation (which can cause a shock of fire hazard). It will protect every boat plugged into 30A power, even if you have a galvanic isolator. Constantly monitors for unsafe corrosion activity and reverse polarity Warns of unsafe reverse polarity conditions and destructive galvanic activity Will benefit any boat connected to 30A shore power. Plug-in and test your Shore Power. The red and green LED indicates whether you have a safe or unsafe shore power system. This is a Hot Seller & Great Gift for individual boaters.