A capacitive level-sensor device for detecting the level of a medium contained in a container, in particular a tank, the device comprising: - a circuit substrate made of electrically insulating material, which extends longitudinally according to a level-sensing axis, the circuit substrate having a first major face and a second major face opposite to one another, which define therebetween a substrate thickness, and two opposite longitudinal edges (20c, 20d), which define therebetween a substrate width, the circuit substrate having a first longitudinal end and a second longitudinal end; - a first array of electrodes or capacitive elements on a sensing region of the circuit substrate that includes said first longitudinal end, the first array of electrodes or capacitive elements comprising at least one first series of first electrodes coplanar to one another at the first major face of the circuit substrate, the first electrodes being spaced apart from one another along the level-sensing axis; - a circuit, which comprises circuit components (17, 24a, 25, 26, 27a, 27b, CT) associated to a second region of the circuit substrate that is axially comprised between said second longitudinal end and the first series of electrodes, the circuit components (17, 24a, 25, 26, 27a, 27b, CT) preferably including at least one of electrical-connection elements (24a, CT), electrical terminals, and a control unit having a plurality of first inputs electrically connected to which are the first electrodes; - a casing body, which comprises at least: a sensing portion, which is electrically insulating and fluid-tight and covers at least the sensing region of the circuit substrate; and a mounting portion, which covers at least partially the second region of the circuit substrate and is configured for fluid-tight fixing at an opening of the container, wherein the sensing portion and at least part of the mounting portion comprise at least one material overmoulded on at least part of the circuit substrate, wherein the at least one overmoulded material of the mounting portion defines a seat for an annular seal element, characterized in that the second region of the circuit substrate includes at least one restricted substrate portion, having a substrate width (Wr) smaller than the substrate width of the sensing region, in that at least part of the at least one restricted substrate portion extends axially in the mounting portion, and in that the seat for the annular sealing element is in a position corresponding to the at least one restricted substrate portion of the second region of the circuit substrate. - a circuit substrate made of electrically insulating material, which extends longitudinally according to a level-sensing axis, the circuit substrate having a first major face and a second major face opposite to one another, which define therebetween a substrate thickness, and two opposite longitudinal edges (20c, 20d), which define therebetween a substrate width, the circuit substrate having a first longitudinal end and a second longitudinal end; - a first array of electrodes or capacitive elements on a sensing region of the circuit substrate that includes said first longitudinal end, the first array of electrodes or capacitive elements comprising at least one first series of first electrodes coplanar to one another at the first major face of the circuit substrate, the first electrodes being spaced apart from one another along the level-sensing axis; - a circuit, which comprises circuit components (17, 24a, 25, 26, 27a, 27b, CT) associated to a second region of the circuit substrate that is axially comprised between said second longitudinal end and the first series of electrodes, the circuit components (17, 24a, 25, 26, 27a, 27b, CT) preferably including at least one of electrical-connection elements (24a, CT), electrical terminals, and a control unit having a plurality of first inputs electrically connected to which are the first electrodes; - a casing body, which comprises at least: a sensing portion, which is electrically insulating and fluid-tight and covers at least the sensing region of the circuit substrate; and a mounting portion, which covers at least partially the second region of the circuit substrate and is configured for fluid-tight fixing at an opening of the container, a sensing portion, which is electrically insulating and fluid-tight and covers at least the sensing region of the circuit substrate; and a mounting portion, which covers at least partially the second region of the circuit substrate and is configured for fluid-tight fixing at an opening of the container, wherein the sensing portion and at least part of the mounting portion comprise at least one material overmoulded on at least part of the circuit substrate, wherein the at least one overmoulded material of the mounting portion defines a seat for an annular seal element, characterized in that the second region of the circuit substrate includes at least one restricted substrate portion, having a substrate width (Wr) smaller than the substrate width of the sensing region, in that at least part of the at least one restricted substrate portion extends axially in the mounting portion, and in that the seat for the annular sealing element is in a position corresponding to the at least one restricted substrate portion of the second region of the circuit substrate.