into the closed position 16 when it detects that the hand is removed from the measurement volume 12 i e from the window 3 the smoker gap 14 is dimensioned for example with 3 5 cm clear width between the upper edge of the window 3 and the upper window seal in such a way that it is ensured that smoke is effectively drawn out the sensor 9 is in particular an infrared camera the control unit 6 is configured here to determine a temperature measured variable referred to below as temperature measured value t m by means of the infrared camera and to detect the approaching of the vehicle occupant 39 s hand into the measurement volume 12 on the basis of this temperature measured value t m the temperature measured value t m represents here in particular the maximum value or an average value of the temperature in the measurement volume 12 in specific terms in a first method step 20 the control unit 6 according to fig2 checks when the window 3 is closed whether the detected temperature measured value t m exceeds a temperature threshold t s which is characteristic of the presence of a glowing cigarette or cigar within the measurement volume 12 the temperature threshold t s is for example 200 u00b0 c and is here significantly above the body surface.