Body temperature is routinely monitored in clinical settings with infrared ear thermometers which measure the infrared energy emitted from the patient's eardrum in a calibrated length of time. A short tube with a protective sleeve is inserted into the ear, and a shutter is opened to allow radiation from the tympanic membrane to fall on an infrared detector for a period which is typically from 0.1 to 0.3 seconds in the varieties surveyed. The device beeps when data collection is completed and a readout of temperature is produced on a liquid crystal display.
source:GTE Medical