The present invention relates to device system and method for unobtrusively and reliably detecting apnoea of a subject (2). The proposed device comprises an input unit (11) for receiving image data of subject said image data including a sequence of images over time a cardiac activity extraction unit (12) for extracting from said image data a cardiac activity signal representing the subject s cardiac activity from a skin area of the subject using remote photoplethysmography a motion signal extraction unit (14) for extracting from said image data a motion signal representing motion of a subject s body part caused by breathing of the subject an analysis unit (16) for determining the similarity between said cardiac activity signal and said motion signal and an decision unit (18) for detecting apnoea of the subject based on the determined similarity.