Have you ever returned home from a vacation, business trip, or a weekend away with the family and seen your digital clocks flashing the wrong time? You quickly discover that you had a power outage while you were away, but it’s nearly hard to determine when or how long it lasted. It is also impossible to say how long the food in your freezer may have thawed, been destroyed, and then frozen again.

Or is it? In response to Hurricane Matthews, which raced across sections of the United States in 2016, a woman called Sheila Pulanco Russell posted a brilliant technique on her Facebook wall for anyone who was forced to flee their property. However, the tactic is also useful in the event of an extended absence from your house, as it will alleviate your concerns about whether or not the food in your freezer is safe to consume or should be discarded immediately.

The method is a miraculous mix of three simple but efficient things that everyone has at home: a mug, a penny, and some tap water. “For those of you fleeing from the shore, I just heard a fantastic tip. It’s known as the one-cup tip. You store a cup of water in your freezer. Freeze it solid, then place a quarter on top and store it in your freezer.

That way, when you return after being evacuated, you’ll know whether your food went entirely rotten and was just refrozen, or if it remained frozen while you were gone. If the quarter has fallen to the bottom of the cup, it indicates that all of the food has defrosted and should be discarded. However, if the quarter is on top or in the center of the cup, your food may still be fine. It’s also a good idea to have this in your freezer at all times, so if you lose power for any reason, you’ll have this tip on hand.