Product review (4 stars): Could help if you think you have a problem
First off you should be using a thermometer to begin with, the ideal freezer temperature is zero degrees. This won't tell you that. This could come in handy If you think your freezer is not working properly and your food thaws out during strange times then theoretically the ball will drop and freeze at the lower location. But if it gets that bad seems like you would notice your ice cream is soft too. It is cheap and simple but don't rely on it for checking the accuracy of the temperature - do that as well.