Storm evacuation tip

I saw this on Facebook shared by a friend that lives in Florida:
Sheila - Lumberton, NC
For those of you that are evacuating from the coast, I just heard a great tip. It's called the one cup tip. You put a cup of water in your freezer. Freeze it solid and then put a quarter on top of it and leave it in your freezer. That way when you come back after you've been evacuated you can tell if your food went completely bad and just refroze or if it stayed Frozen while you were gone. If the quarter has fallen to the bottom of the cup that means all the food defrosted and you should throw it out. But if the quarter is either on the top or in the middle of the cup then your food may still be ok. It would also be a great idea to leave this in your freezer all the time and if you loose power for any reason you will have this tip to fall back on.