A vehicle seat has an upper body side protection device that is integrated in the back rest. The novel device includes a diaphragm adapted to deform in response to a pressure applied thereto, and a retractable support adapted to support the diaphragm during periods of non-operation. The energy at the input is derived from an AC mains voltage at a mains frequency. The groove may also contain an anti-reflecting layer to further increase the difference in reflectivity.