The present invention relates to a device, system and method for determining a vital sign of a person. To improve accuracy and reliability of vital sign determination, the device comprises an input unit (20) for obtaining a vital sign related signal of at least a body part of the person, from which a vital sign can be derived, a body part position determining unit (21) for determining if said body part of the person is in contact with a support or not and generating a contact signal indicating if said body part is in contact with the support or not, a quality metric setting unit (22) for setting, based on said contact signal, a quality metric for use in the determination of a vital sign of the person, and a vital sign deriving unit (23) for deriving a vital sign from the obtained vital sign related signal, wherein the set quality metric is used in the derivation of the vital sign and/or in a judgment of the reliability of a derived vital.