They may be relatively small, single-purpose hand-held instruments that are simple to operate and are designed to measure the concentration of bilirubin in the blood. ... Cutaneous bilirubinometers do not require a blood sample. A light-emitting sensor is placed on the infant's skin (optimally on the forehead or sternum).
 
How does Bilirubinometer work?
 
High correlation between cutaneous bilirubin and TSB form the basis of Transcutaneous Bilirubinometry. These meters work by directing light into the skin of the neonate and measuring the intensity of specific wavelength that is returned. ... These are analyzed by a microprocessor to generate a serum bilirubin value.