The device (50) includes at least one electronic circuit (52) and a battery (53) provided for powering the circuit, wherein the circuit and the battery are included in a block of hydrophobic material, for example a block of resin (51). The battery is, for example, an inductively charged battery and the device can include optical sockets (56a, 56b, 56c) for fiber-optic cables, so as to avoid all contact of metal parts with water. Such a device is especially suitable for a buoyancy compensator vest, for use as a “stabilizer during immersion” and as a “closed-circuit rebreather”.