A wearable device for continuous health monitoring, the device comprising: a. a band for conforming to a first body part of a subject; b. 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 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; ii. 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; c. a controller unit configured to derive a PPG signal from the acquired sequence of images according to a first process in the contact mode and according to a second process 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 indicative of whether the device is to operate in the contact mode or the non-contact mode, to determine if the PPG signal is to be derived according to the first process or the second process depending on whether the at least one pre-determined condition is fulfilled, and to derive the PPG signal from the acquired sequence of images according to said determined process. a. a band for conforming to a first body part of a subject; b. 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 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; ii. 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; i. wherein in the contact mode the imaging unit is in substantial close 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; ii. 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; c. a controller unit configured to derive a PPG signal from the acquired sequence of images according to a first process in the contact mode and according to a second process 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 indicative of whether the device is to operate in the contact mode or the non-contact mode, to determine if the PPG signal is to be derived according to the first process or the second process depending on whether the at least one pre-determined condition is fulfilled, and to derive the PPG signal from the acquired sequence of images according to said determined process.