Modular physiological sensors that are physically and/or electrically configured to share a measurement site for the comfort of the patient and/or to ensure proper operation of the sensors without interference from the other sensors. The modular aspect is realized by providing outer housing shapes that generally conform to other physiological sensors; mounting areas for attachment of one sensor to another sensor; providing release liners on the overlapping sensor attachment areas; and/or providing notches, tabs or other mechanical features that provide for the proper placement and interaction of the sensors.