The invention includes a thermometer with a backlight and a method for lighting the backlight. The thermometer has temperature sensing tip, a processor taking temperature readings and determining a sensed temperature reading of the living being from the temperature sensing tip. The thermometer also includes a display and a backlight for lighting the display. The backlight is activated upon a command from the processor and the processor determines whether a decrease in the temperature readings exceeds or is equal to a predetermined threshold in order to activate the backlight. The method embodiment can includes the steps of using the processor to monitor a temperature change indicated by a temperature sensing element. The processor then detects a temperature decrease and activates a first color light emitting element to backlight a display if the temperature decrease exceeds or equals a predetermined threshold.