System (10, 10') for determining vital signs of a subject comprising: a device for determining vital signs of a subject, a first light source arranged for illuminating a front side of a region of interest of the subject with light in at least a first wavelength range to obtain reflected light that is reflected from the region of interest, a second light source (24, 25) arranged for transmitting light in at least a second wavelength range different from the first wavelength range from a rear side of the region of interest through the region of interest to obtain transmitted light that is transmitted through the region of interest, wherein the first and and second light sources are configured to illuminate the region of interest and to transmit light through the region of interest at least temporarily simultaneous, and wherein the device comprises: - a single detection unit arranged for contactless detection of light in at least two different wavelength ranges from the region of interest of the subject and for contactless detection of the reflected light and the transmitted light from the front side of the region of interest of the subject, wherein said detection unit is configured to detect a first light portion in the first wavelength range from the reflected light and to detect a second light portion in the second wavelength range from the transmitted light, wherein said detection unit is configured to detect said first light portion and said second light portion simultaneously, - a processing unit for deriving plethysmography, PPG, signals from the detected light for said at least two different wavelength ranges, and - an analysis unit for deriving a vital sign from the PPG signals for at least two different wavelength ranges. a device for determining vital signs of a subject, a first light source arranged for illuminating a front side of a region of interest of the subject with light in at least a first wavelength range to obtain reflected light that is reflected from the region of interest, a second light source (24, 25) arranged for transmitting light in at least a second wavelength range different from the first wavelength range from a rear side of the region of interest through the region of interest to obtain transmitted light that is transmitted through the region of interest, wherein the first and and second light sources are configured to illuminate the region of interest and to transmit light through the region of interest at least temporarily simultaneous, and wherein the device comprises: - a single detection unit arranged for contactless detection of light in at least two different wavelength ranges from the region of interest of the subject and for contactless detection of the reflected light and the transmitted light from the front side of the region of interest of the subject, wherein said detection unit is configured to detect a first light portion in the first wavelength range from the reflected light and to detect a second light portion in the second wavelength range from the transmitted light, wherein said detection unit is configured to detect said first light portion and said second light portion simultaneously, - a processing unit for deriving plethysmography, PPG, signals from the detected light for said at least two different wavelength ranges, and - an analysis unit for deriving a vital sign from the PPG signals for at least two different wavelength ranges. - a single detection unit arranged for contactless detection of light in at least two different wavelength ranges from the region of interest of the subject and for contactless detection of the reflected light and the transmitted light from the front side of the region of interest of the subject, wherein said detection unit is configured to detect a first light portion in the first wavelength range from the reflected light and to detect a second light portion in the second wavelength range from the transmitted light, wherein said detection unit is configured to detect said first light portion and said second light portion simultaneously, - a processing unit for deriving plethysmography, PPG, signals from the detected light for said at least two different wavelength ranges, and - an analysis unit for deriving a vital sign from the PPG signals for at least two different wavelength ranges.