The present invention relates to a device system and method for determining a vital sign of a subject. To reduce the effects of subject motion in particular of ballistocardiographic motion the device comprises an input interface (30) for obtaining at least two radiation signals each radiation signal being acquired from different skin regions of the subject by detecting radiation reflected from or transmitted through the respective skin region in response to irradiation an extraction unit (31) for extracting photoplethysmography (PPG) signals from the obtained radiation signals to obtain at least one PPG signal per skin region an evaluation unit (32) for determining first weights for said skin regions depending on the relative and/or absolute strength of fundamental frequency and/or one or more harmonics in the spectrum of the PPG signal of the respective skin region a combination unit (33) for combining two or more PPG signals of different skin regions based on their respective first weights to obtain a combined PPG signal and a vital sign determination unit (34) for deriving a vital sign from the combined PPG signal.
