Temperature of a subject is continuously monitored using a remote sensor assembly mounted in a subject's ear canal. The remote assembly connects to a display housing which contains the temperature display and supports electronics for responding to the sensed radiation. In one configuration, the major components of the remote assembly include a radiation detector, a plug structure and a flexible extension. The radiation detector has a thermopile and a first temperature sensor in close thermal contact with a thermopile junction. The flexible extension connects the radiation detector with the plug structure. Because the flexible extension bends to the contours of an ear canal, the remote sensor assembly extends well into a subject's ear canal without discomfort. The plug structure is molded to fit securely in the concha region of an ear canal and includes a second temperature sensor which senses the temperature therein. Continuous temperature measurements are determined by combining the sensed temperature for the thermopile and the first and second temperature sensors and converting this combined signal to a temperature indication. In another configuration, the remote sensor assembly has a radiation detector and an ear-piece shaped to fit behind the subject's ear. The ear-piece replaces the plug structure for this configuration and provides the same functions. The flexible extension connects the radiation detector and the ear-piece. A hollow adapter shaped to fit in the concha region of an ear is positioned over a portion of the extension. The position of the adapter on the extension may be varied such that the depth of penetration of the radiation detector into the ear canal is adjustable.