Why put a coin in a glass of water in the fridge?

How a Coin in a Glass Can Save Your Frozen Food

Ever come home after a storm or power outage and wonder if your freezer stayed cold enough? There’s a clever, low-tech trick that can help you find out—just drop a coin in a glass of water and freeze it.

Here’s how it works: Fill a small glass with water, place a coin on top of a floating piece of ice, then put it in the freezer. Or better yet, freeze the water first, then place the coin on the solid surface and return it to the freezer. If the power goes out, the temperature will rise and the ice will begin to melt. As it does, the coin will sink into the glass. When the power returns and the water refreezes, the coin remains trapped inside—no longer on top, but embedded somewhere within or at the bottom.

This simple setup acts like a silent alarm. If you come back and the coin is still right on top, your freezer likely stayed cold. But if it’s halfway down or sitting at the bottom, that means your food may have thawed—possibly reaching unsafe temperatures.

It’s not just about convenience; it’s about safety. Perishable foods like meat, dairy, and frozen meals can spoil quickly if they’re not kept consistently cold. While freezers often keep things safe during short outages, you won’t always know just how long they were warm—especially if you weren’t home.

The coin-in-glass trick won’t replace a thermometer, but it’s a smart, no-cost way to get peace of mind. Best of all, it requires nothing more than items you already have in your kitchen. So before the next storm rolls in, it might be worth setting one up—just in case.