Have you ever returned from a trip to find your digital clock reset? This often means a power outage occurred, but it’s hard to know when and for how long, making it difficult to tell if your food is still safe.

A woman named Sheila Pulanco Russell shared a great tip on Facebook to help determine if food in your freezer is still good after a power outage.

“For those of you that are evacuating from the coast, I just heard a great tip. It’s called the one cup tip,” Sheila writes. “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.”

This simple trick helps you know if your food has spoiled. “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.”

Sheila suggests leaving the cup in your freezer all the time for peace of mind. “If you don’t feel good about your food, just throw it out. The main thing is for all to be safe.”

Please share this tip with family and friends—it might save someone’s life.