The transmission mode is capable of obtaining a relatively good signal, but the measurement site may be limited. To be effective, the sensor must be located on the body at a site where transmitted light can be readily detected, such as the fingertip, nasal septum, cheek, tongue, or earlobe. Sensor placement on the nasal septum, cheek or tongue is only effective under anesthesia. The fingertip and earlobe are the preferred monitoring positions; however, these sites have limited blood perfusion. In addition, the fingertip and earlobe are more susceptible to environmental extremes, such as low ambient temperatures (e.g., for military personnel or athletes in training). The greatest disadvantage is that the fingertip sensor interferes with daily activates.