**Keep one or two ice cubes in a sealed plastic bag in the freezer.** If they melt and refreeze into a puddle-shaped lump, you have evidence of thawing—even after power returns and everything freezes again. [University of Nebraska Extension](https://food.unl.edu/article/how-tell-if-your-freezer-power-was-when-you-were-away/) recommends this method.

This indicator cannot tell you the highest temperature reached or how long food stayed warm. For that, use a battery-powered temperature logger with a freezer-rated probe. A maximum-memory thermometer records the highest temperature; a logger also records the duration. **The current freezer temperature alone cannot establish what happened during the outage.**

For deciding what to keep, food temperature and time matter:

- Food checked before it has cooled again can generally be refrozen or cooked if it still contains ice crystals or is at **40°F (4°C) or below**.
- Discard perishable foods such as meat, poultry, fish, and prepared meals if they were above **40°F (4°C) for more than two hours**.
- If food has already refrozen and its temperature history is unknown, its frozen condition cannot establish safety. Never taste food to check it.

Crossing water’s freezing point, **32°F (0°C)**, alone does not mean food must be discarded. Consult the [FoodSafety.gov outage chart](https://www.foodsafety.gov/food-safety-charts/food-safety-during-power-outage) for food-specific guidance.