A capacitive occupant sensor for a seat has a dielectric in the form of a fluid-filled elastomeric bladder, and the sensor includes a primary region that is subjected to occupant force and a secondary region that is shielded from occupant force. A semiconductor integrated circuit device comprises a plurality of word lines, a plurality of bit-lines, a plurality of ordinary memory cells, an access control circuit, a plurality of sense-amplifiers, first and second replica bit-lines, first and second replica memory cells, and first and second logic circuits. A non-return valve is provided to block a flow of impregnating fluid in the direction toward the feed end. A conductive body is disposed in the accommodation chamber and is movable between a closed circuit state that bridges the contact portions of at least two conductive terminals and an open circuit state that does not bridge the contact portions of any two conductive terminals.