The present invention relates to a monitoring device (10) comprising a light source (14) for emitting light into a body part (12) of a living being; a light sensor (18) for receiving light (16) including an ambient light component (30) and a measurement light component (32) resulting from interactions of said emitted light with said body part (12) and for generating an output signal (34), wherein a transfer function describes the relation between the output signal (34) and the received light; an ambient light cancellation unit (20) for separating the output signal (34) into a first signal portion (36) corresponding to the ambient light component (30) and a second signal portion (38) corresponding to the measurement light component (32); and an ambient light modulation removal unit (22) for compensating a variation of the ambient light component (30) by demodulating the second signal portion (38) based on the transfer function (f) and the first signal portion (36) to generate a measurement signal (40).