A device commonly used to measure temperature is a thermometer. Thermometers can operate on various principles, including the thermal expansion of liquids, electrical resistance, or infrared radiation. Traditional mercury or alcohol thermometers work by having a liquid expand or contract in response to temperature changes, providing a reading on a scale. Digital thermometers use electronic sensors to deliver quick and accurate readings. Thermometers are widely utilized in various fields, from meteorology to medicine, allowing us to monitor temperatures in environments, body heat, and other applications critical for health and safety.