A wearable device for continuous health monitoring, the device comprising: a band for conforming to a first body part of a subject; an imaging unit, the imaging unit being connected in the band, wherein the imaging unit is configured to acquire a sequence of images from the subject's body, wherein the device is operable in a contact mode and in a non-contact mode, i. wherein in the contact mode the imaging unit is in substantial close 5 proximity to the first body part of the subject so as to acquire the sequence of images of an area of the first body part; wherein in the non-contact mode the imaging unit is in a remote position to acquire the sequence of images of a second body part of the subject; a controller unit configured to derive a PPG signal from the acquired sequence of images according to a first process when the device is in the contact mode and according to a second process when 10 the device is in the non-contact mode, the PPG signal being indicative of the health of the subject; wherein the controller unit, during operation of the wearable device, is configured to check at least one pre-determined condition in order to determine if the PPG signal is to be derived according to the first process or the second process.