A thermometer is a device to measure temperature. Digital thermometers have one end as probe to sense the temperature and this is converted in to current which is then measured by an Amperage meter / Current Meter which is digital.
Temperature varies in various parts of human body. Hence specific thermometers have been designed to facilitate taking temperature from specific parts e.g., for infants temperature has to be taken in the ears which depict the exact temperature of the body.
Non contact thermometers work on radiation rather than conduction mode of heat transfer from a hot body to cold body. These are useful to contain transmission of infection and also to measure the temperature of infants where holding the thermometer against body is difficult.