A sensor for detecting and measuring a load pressure applied to a support device comprises at least one capacitive cell including a flat condenser comprising at least one layer of a compressible insulating dielectric material interposed between two layers of conductive material. A support device capable of supporting the body of a person comprises at least one top layer composed of a plurality of air-filled inflatable cells communicating with inflation elements, characterized in that it comprises a sensor, of which said condenser is disposed under said top layer and connected to an electronic control and regulation device capable of controlling inflation or deflation elements.