There are a wide range of thermometers including:

Every kitchen needs a probe thermometer to monitor temperature inside dishes. Infra-red guns make it very easy to measure external temperatures but don’t necessarily provide an accurate indication of the internal temperature.

A food business must, at food premises where potentially hazardous food is handled, have a temperature measuring device that is readily accessible and can accurately measure the temperature of potentially hazardous food to +/- 1ºC.
Australian & New Zealand Food Standards Code
3.2.2, Division 6, 22

Thermometers should also be kept where ever potentially hazardous foods are stored.

These are just a few ways to monitor food.