Have you ever come home from vacation, business trip or maybe a weekend away with the family – and noticed your digital clocks flashing the wrong time?

You quickly realize that you had a power outage while you were away, but it’s basically impossible to tell when it occurred or how long it lasted. It’s therefore also impossible to tell just how long the food in your freezer may have thawed, gotten destroyed, and then frozen again.

Or is it?

In connection with Hurricane Matthews which swept over parts of the United States in 2016, a woman named Sheila Pulanco Russell shared a clever trick on her Facebook wall with anyone who was forced to evacuate their home.

But the trick is certainly also good to know in case of any prolonged departure from your home – and will ease your mind about whether or not the food in your freezer is good to eat – or best be thrown out right away.

The trick lies in the magical combination of three simple but effective tools everyone already has at home: a mug, a coin and some tap water.