The present disclosure relates to sensors for use on a patient's ear. The sensors as provided may include a moldable member, such as a putty. The moldable member may be molded in place to affix the optical components of the sensor to a patient's ear tissue. For example, the moldable member may be sculpted around a curvature of a patient's earlobe. In particular embodiments, the moldable member may be activated, e.g., hardened, by exposure to particular temperatures or by exposure to light.