Sensor designs or shapes to facilitate the placement of sensors on a patient are provided. For example, a first sensor may include a sensor body having a keyed interface region that is configured to align with a complementary keyed interface region of second sensor. Such sensors may also include various features to further facilitate the positioning of the sensors on the patient tissue and the positioning of the sensors with respect to one another. For example, the first sensor may include indicia relating to the second sensor having the complementary keyed interface region.
