A sensor cartridge according to embodiments of the disclosure is capable of being used with a non-invasive physiological sensor. Certain embodiments of the sensor cartridge protect the sensor from damage, such as damage due to repeated use, reduce the need for sensor sanitization, or both. Further, embodiments of the sensor cartridge are positionable on the user before insertion in the sensor and allow for improved alignment of the treatment site with the sensor. In addition, the sensor cartridge of certain embodiments of the disclosure can be configured to allow a single sensor to comfortably accommodate treatment sites of various sizes such as for both adult and pediatric applications.