So imagine that you’re finally on vacation, actually feeling relaxed for once in your life. Whether you’re sunbathing on a beach or hiding in a cabin with no phone reception, you’ll have escaped from your home. This means you’re definitely not thinking about your refrigerator. At least this would be your state of mind, but you might want to consider it.

As dramatic as it sounds, if you lose power while you’re gone for even a little bit, it can affect your refrigerator. Sometimes, it affects it in ways that are not terribly evident. This happened to my best friend and all her food spoiled, it was a disaster. Let’s think about it: the power kicks off for a few hours, and everything in your fridge warms up, including your meat and dairy. The power comes back on, everything looks fine when you come home, but everything is not fine. You would have no idea that your food sat at room temperature long enough to be a breeding ground for something vile. Then you end up eating it because you think you’re okay, thinking you no longer have a refrigerator full of room-temperature food.

That is where this weird freezer trick comes in. It’s incredibly simple, outrageous in how simple it is, and yet fairly clever. It has been making the rounds a few months on Facebook. I suspect Sheila Pulanco Russell will get the credit (wherever you are Sheila). It’s one of those things that you think you will never need until you do.

So here is the trick. You take your average cup and fill it with water. Put it in the freezer until it freezes solid. Then place a coin on top of the frozen water. That’s it. Just leave it there before heading out on vacation.

When you return, the cup will basically tell you what happened while you were gone. If the coin is still right there on top, you’re in the clear. That means the freezer stayed cold this whole time, and your food is in a good spot. If, however, the coin has sunk to the bottom or even sunk somewhere in the middle, that’s a bad sign. That means the ice melted, or in other words the freezer warmed, and at some point the power went out. Even if it refroze, what is essentially a brief-thaw window could be plenty of time to make your food unsafe.

It’s a weirdly comforting hack, since you have such a low-effort way to check. Especially since, again, you really wouldn’t have any other obvious sign unless you had something spoiled or dripping. A lot of the time, you just wouldn’t know.

And by the way, this isn’t just for vacations. This came in handy when we had to leave the house last year because of wildfires. It might be useful in the case of sudden evacuations from flooding, storms, or whatever disaster might work its way through your area. It’s already a hassle to find out you’re leaving your house in a hurry. Therefore, the last thing you want to deal with when you return is guessing if the food you left is safe. This at least gives you some peace of mind.

Plus, let’s be honest. This is the kind of hack where you can tell your parents or neighbors about it. They’ll be equal parts impressed and annoyed that they didn’t think of it. It’s one of those old-timey tricks that seems like something your grandma would do. Yet, it will also hold up in 2025 when we still don’t have smart fridges telling us when the ham has gone bad.

Of course, if you want to go all out on being a prepper, you could also just dump anything perishable before a long trip. Or, load the freezer with batteries and sensors and all that technology bullshit. But most of us just want to keep it simple. This coin-and-cup thing? That’s about as simple as it gets.

So the next time you are heading out the door with your suitcase zipped and your lights turned off, take the additional 30 seconds to toss a cup of water in the freezer. Then place a coin on top. It’s a low-effort, kind of a brilliant hack, and way better than trying to guess if that leftover chicken is going to poison you.