Abstract: The invention pertains to an electric device which can be started by immersion in a liquid by way of two electrodes. It includes a first circuit having two electrodes in series with a first voltage source and the coil of a first relay, for controlling a second circuit having in series a second voltage source, a second relay and the contact of the first relay. The second circuit also is connected to use terminals for an external load, the voltage at the use terminals of the circuit being equal to the sum of the voltages from the first and second voltage sources. The device can be applied to power submersible buoys and to detect the presence of a liquid.