Your thermometer shows you whether you have a fever and if so, how high it is. There are classic glass thermometers and digital thermometers. The latter also includes infrared thermometers. A clinical thermometer measures your body temperature between 35 and 42 degrees and should always show your maximum temperature. Mercury thermometers, for example, fulfil this criterion.
However, since a thermometer filled with mercury easily becomes defective and is difficult to dispose of, these glass thermometers often contain galinstan as a liquid instead. But also digital thermometers with batteries are often used, because they show your value quickly and legibly on an LED display.
Don't forget the infrared thermometers, which measure the radiation by means of a sensor without contact or by touch.