The Cambridge Hydro Switch™ detects moisture caused by an accumulation of air conditioning condensate or due to a leak. Once detected, the closed circuit controlling the system is immediately disconnected, preventing flooding and any property damage. Multiple hydro switches may be connected to expand the coverage area if it is within the electrical limits of the power supply. The hydro switch incorporates isolated relay contacts for installations with electronic control boards where breaking one lead from the transformer is not possible. It also includes an extra open circuit that may be used to operate an alarm device.