A detection and/or control device for a liquid-conducting appliance or system comprises:—a hydraulic body (2) defining a duct (3) for a flow of a liquid, the duct (3) having an inlet (4) and an outlet (5), and being made at least in part of an electrically insulating material;—a flow sensor located at least in part on the hydraulic body (2), which comprises:—an electromagnetic arrangement, configured for generating an electromagnetic field through said part of the duct (3), in a direction transverse to the flow of the liquid, —a detection arrangement, which comprises at least two electrode units (20) for detecting a potential difference induced by the flow of the liquid through the electromagnetic field, the at least two electrode units (20) being arranged for being in contact with the liquid in a respective working position. The hydraulic body (2) has at least two through openings on two opposite sides (3a, 3b) of the duct (3), at least partially inserted in each of which is a corresponding electrode unit (20), in such a way that, in the respective working positions, the electrode units (20) are substantially aligned or opposed to one another. The device (1) moreover comprises sealing means at each through opening, which are configured for preventing leakage of the liquid from the duct (3) through the corresponding through opening. The sealing means (22) are associated to, or integrated in, a respective electrode unit (20), in such a way that said sealing means (22) of an electrode unit (20) can be positioned relative to one said through opening by means of one and the same movement of insertion of the respective electrode unit (20) into the corresponding through opening.