Thermometers use the principle of changing liquid volume when temperature changes, with mercury or alcohol traditionally used as the filling. However, mercury use is now prohibited in many areas, so alternatives like galinstan alloy are being explored. Thermometers can also operate electrically by measuring conductor resistance changes with temperature, optically by detecting luminance or spectrum parameter changes, or through infrared detection without direct contact. Technical thermometers filled with liquid are commonly used across many industries and aspects of daily life.