The device used to measure temperature is called a thermometer. Various types exist, including mercury thermometers, digital thermometers, and infrared thermometers. Traditional mercury thermometers operate by measuring the expansion of mercury in a glass tube as temperatures rise or fall. Digital thermometers, commonly used in medical and everyday applications, provide quick readings by using electronic sensors. Infrared thermometers measure temperature from a distance by detecting infrared radiation emitted from objects. Thermometers are essential in numerous fields, including healthcare, meteorology, and industry, helping to monitor and control temperatures effectively.