It is part of the advancement of technology where the mercury thermometer began to be replaced by other ways that are relatively more secure.
Digital thermometers are usually equipped with a sound (eg beep) that will tell you that temperature measurement has been completed. Measurement is generally the same as the measurement using conventional thermometers (mercury), it’s just that you do not need to look at the clock to know when a temperature measurement is complete.
However, make it a habit to read first the instructions supplied by the manufacturer that the thermometer. Because maybe you buy a thermometer that require different ways to use.