Abstract: This invention relates to an apparatus for detecting the presence of a specific concentration of a conducting medium (water) in an insulating medium (oil) wherein the water/oil mixture forms an emulsion containing discrete droplets of water. A probe containing two electrodes, the first of which has a flat surface and the second of which is cone-shaped having a vertex directed at the flat surface, is immersed into the emulsion. A pulsating dc voltage is applied to the first electrode producing a static electrical charge which repels the insulating medium while having no effect on the conducting medium, causing droplets of the conducting medium to migrate towards and accumulate in the area between the electrodes. When a sufficient number of droplets have accumulated, a conductive path is formed between the electrodes causing an alarm to be generated.