Seat comprising: - a cushioning made from a flexible material comprising a blind cavity, this blind cavity comprising: • an opening opening out on one side of the cushioning, • a base located on the side opposite the opening, and • lateral walls extending from the periphery of the base as far as the periphery of the opening, - an instrumented unit made from flexible material received inside the cavity, this instrumented unit comprising: • an interior face turned toward the base of the cavity, • an exterior face located on the side opposite the interior face and directly exposed to the exterior of the cushioning, • lateral faces that extend from the periphery of the interior face as far as the periphery of the exterior face, these lateral faces being shaped such as to hold the instrumented unit wedged inside the cavity by interaction of form with the lateral walls of the cavity, and • an electrical device, characterized in that: - the instrumented unit comprises an oblong housing, this oblong housing comprising lateral flanks that extend principally toward the interior of the instrumented unit from an inlet located on one of the lateral faces of the instrumented unit, this inlet being capable of allowing the insertion of the electrical device inside the housing, and - the electrical device is entirely received inside this housing. - a cushioning made from a flexible material comprising a blind cavity, this blind cavity comprising: • an opening opening out on one side of the cushioning, • a base located on the side opposite the opening, and • lateral walls extending from the periphery of the base as far as the periphery of the opening, - an instrumented unit made from flexible material received inside the cavity, this instrumented unit comprising: • an interior face turned toward the base of the cavity, • an exterior face located on the side opposite the interior face and directly exposed to the exterior of the cushioning, • lateral faces that extend from the periphery of the interior face as far as the periphery of the exterior face, these lateral faces being shaped such as to hold the instrumented unit wedged inside the cavity by interaction of form with the lateral walls of the cavity, and • an electrical device, characterized in that: - the instrumented unit comprises an oblong housing, this oblong housing comprising lateral flanks that extend principally toward the interior of the instrumented unit from an inlet located on one of the lateral faces of the instrumented unit, this inlet being capable of allowing the insertion of the electrical device inside the housing, and - the electrical device is entirely received inside this housing. • an opening opening out on one side of the cushioning, • a base located on the side opposite the opening, and • lateral walls extending from the periphery of the base as far as the periphery of the opening, - an instrumented unit made from flexible material received inside the cavity, this instrumented unit comprising: - an instrumented unit made from flexible material received inside the cavity, this instrumented unit comprising: • an interior face turned toward the base of the cavity, • an exterior face located on the side opposite the interior face and directly exposed to the exterior of the cushioning, • lateral faces that extend from the periphery of the interior face as far as the periphery of the exterior face, these lateral faces being shaped such as to hold the instrumented unit wedged inside the cavity by interaction of form with the lateral walls of the cavity, and • an electrical device, characterized in that: - the instrumented unit comprises an oblong housing, this oblong housing comprising lateral flanks that extend principally toward the interior of the instrumented unit from an inlet located on one of the lateral faces of the instrumented unit, this inlet being capable of allowing the insertion of the electrical device inside the housing, and - the electrical device is entirely received inside this housing. - the instrumented unit comprises an oblong housing, this oblong housing comprising lateral flanks that extend principally toward the interior of the instrumented unit from an inlet located on one of the lateral faces of the instrumented unit, this inlet being capable of allowing the insertion of the electrical device inside the housing, and - the electrical device is entirely received inside this housing.