The present invention relates to a device for monitoring a vital sign of a subject (14) when attached to the subjects body. The device (12, 12, 12", 12" ) comprises an optical sensor arrangement (18) including a light source (20) for emitting light into tissue of the subject, a light sensor (22) for receiving at least part of the emitted light after an interaction of the emitted light with the tissue and an evaluation unit (24) for deriving an optical monitoring signal from the received light being indicative of the vital sign of the subject (14). The device (12, 12, 12", 12 ") further comprises an auxiliary sensor arrangement (26) different from the optical sensor arrangement (18) for obtaining an auxiliary monitoring signal being indicative of the vital sign of the subject (14). Still further, the device (12, 12, 12", 12" ) comprises a fusion unit (28) for determining an output signal based on the optical monitoring signal and the auxiliary monitoring signal, said output signal being representative of the vital sign of the subject (14) and a control unit (30) for controlling the optical sensor arrangement (18), the auxiliary sensor arrangement (26) and the fusion unit (28). The optical monitoring signal and the auxiliary monitoring signal are indicative of the same vital sign of the subject. The present invention further relates to a corresponding method as well as to a monitoring apparatus (10) including a device as described above.La présente invention concerne un dispositif de surveillance dun signe vital dun sujet (14) lorsquil est fixé au corps du sujet. Le dispositif (12, 12, 12", 12") comprend un agencement de capteur optique (18) comprenant une source de lumière (20) pour émettre de la lumière dans un tissu du sujet, un capteur de lumière (22) pour recevoir au moins une partie de la lumière émise après une interaction de la lumière émise avec le tissu et une unité dévaluation (24) pour dériver un signal de surveillance optique à partir de la lumière reçue
