Patent attributes
A watch having a cover is described. An optical sensor subsystem is attached adjacent to or directly on an interior surface of the cover. In some cases, the optical sensor subsystem includes a substrate to which a light emitter and a light receiver are attached. The light receiver is configured to receive light emitted by the light emitter and reflected from the skin of a person that wears the watch. In some cases, the light emitter and light receiver are separated by a light-blocking wall that abuts the interior surface of the cover. In some cases, a light filter is attached adjacent or directly on the interior surface of the cover, between the cover and the light receiver.