(Anti Media) After creating a path of destruction throughout the Caribbean and knocking power out for at least one million people in Puerto Rico, catastrophic Hurricane Irma is now rapidly approaching Florida.

As Americans continue to evacuate ahead of Irma’s landfall, there is a brilliant and simple life hack going viral across social media. If your home is in the path of a hurricane this month, you’ll want to know if the power went out while you were gone. The way to find out is called the one cup tip.

Here what to do:

  1. Fill a cup with water.
  2. Put it in the freezer until it’s solid.
  3. Place a coin on top.
  4. Leave it in there, and when you return home, check it out.

If the coin is at bottom of the cup of ice when you return home, the power went out, and you’ve got problems. The coin’s descent to the bottom of the cup means the ice melted into water in your freezer, the coin fell through, and then the power came back on, causing the water to freeze back into ice.

This simple trick allows you to know if you should clean out your fridge and throw out likely contaminated food or if everything stayed frozen while you were gone, potentially saving you hundreds of dollars. Even if the coin is in the middle of the cup, your food may still be good because it shows the power was not off long enough to completely melt the ice. During a short power outage, fridges and freezers are usually insulated well enough to keep most food fresh.

Even if you’re not evacuating because of a hurricane, it would still probably be a good idea to keep a cup of ice with a coin on top in your freezer in order to know if — and for how long — your power goes out in the future.