A body temperature detector includes a body having a viewing end, a retaining end, and a disposable cap. The retaining end includes an inward protrusion that expands over a wider portion of an end of the detector and contracts after the retaining end has passed over the wider portion to snugly secure the cap on the detector. An operator can scan the detector across the forehead of the patient and behind at least one ear, and the detector selects a maximum peak temperature of the two scans. The operator can continuously scan the detector from the forehead to behind the ear. Measured temperature is processed to provide a body temperature approximation based on heat flow from the skin surface to ambient temperature.
