A refrigerator thermometer can be an inexpensive way to save real money. If your refrigerator is too warm, food will spoil; if it's too cold, you're paying for more electricity than you need. You should keep your refrigerator at no higher than 40° F and the freezer at 0° F, according to the United States Department of Agriculture.
The threat of food-borne illnesses is another concern with an improperly chilled refrigerator. Microorganisms capable of causing sickness grow very slowly below 40°F. But they rapidly increase between 40° and 140°F.
A refrigerator thermometer is especially useful if your fridge has only a dial thermostat. You can also use it to check that temperatures are still safe on a model with a built-in thermometer. And during a power failure, a thermometer is indispensable. If you've been without power for an extended period, you can use the thermometer to check that temperatures are still safe.
We recently tested three samples of five different thermometers for accuracy, readability, and stability (how quickly the thermometers responded to temperature changes). A thermometer that reacts too quickly to the warm air that enters a refrigerator when the door is opened can give you a misleading reading, making it harder to maintain your refrigerator at the proper temperature.
To test for accuracy, we took five readings with each of the 15 thermometers and compared them with readings from a calibrated thermometer. The readings were averaged and scored. An average of less than 1° F scored excellent, while a difference of 1 degree to 2 degrees scored very good.
All of the thermometers did a very good to excellent job of measuring the temperature, but they were prone to fogging, making them difficult to read.