An apparatus for working in conjunction with a digital sensor, CPU and display of a host device in order to measure blood characteristics that includes a housing configured for association with the host device so as to define between them a chamber into which at least a portion of an appendage of a living being is placed such that a tip of the appendage is deployed adjacent to the digital sensor so as to cover the digital sensor. The chamber substantially encloses the digital sensor. Light from a light source is directed toward the appendage tip, wherein at least some light from the light source is reflected by tissue of the appendage, is received by the sensor and data thereby generated is processed by the CUP to determine the blood characteristics.