**You need something that records warming before the outage.** Once the freezer has cooled again, its current temperature cannot tell you how warm it previously became.

Two practical approaches are:

- **A simple thaw indicator:** Put a few ice cubes in a sealed bag or container and leave it in the freezer. If you later find a puddle—or a solid slab of refrozen water instead of separate cubes—some melting occurred. Another version is to freeze a cup of water, then place a coin on the ice; a sunken coin indicates melting. These show that the indicator thawed, but cannot establish the maximum temperature, duration, or condition of every food package. Intact ice also cannot rule out a brief rise in air temperature above freezing.
- **A recording thermometer:** Use a freezer-rated, battery-powered thermometer with maximum-temperature memory, or preferably a data logger. The former records the highest temperature; the latter records how warm it became and for how long. Reset its memory when you begin monitoring.

**Crossing freezing—32°F (0°C)—does not automatically make food unsafe.** If checked before it has cooled or refrozen after the outage, food that still contains ice crystals or measures **40°F (4°C) or below** can generally be cooked or refrozen, though quality may suffer. [FDA guidance](https://www.fda.gov/food/food-safety-during-emergencies/power-outages-key-tips-consumers-about-food-safety)

Discard perishable foods such as meat, poultry, fish, and prepared meals that have been above **40°F for more than two hours**. Different foods have different discard rules; consult the [FoodSafety.gov chart](https://www.foodsafety.gov/food-safety-charts/food-safety-during-power-outage). If food has already refrozen and you have no temperature history, neither its present temperature nor its frozen appearance proves it stayed safe.