The present disclosure concerns a device for sensing at least one biological parameter (e.g., heart rate, heart rate variability) of a subject, the device comprising a contact surface configured for being brought into a contact with a skin surface of the subject. The device has at least one light source for illuminating the skin surface through the contact surface along an illumination source optical axis with illumination including at least one sensing wavelength, and at least one detector for detecting a response of said illumination at least at said wavelength, from the skin surface through the contact surface along a detector optical axis, and providing signals configured for determining said biological parameter based thereon, said illumination optical axis forming with said contact surface an acute included angle.
