1. The one cup tip
Fill a cup with water and place it in the freezer overnight. Once it has frozen, leave a coin on top. If the coin has sunk to the bottom when you get home, you’ll know that the whole cup has melted and refrozen, and the safety of your food has been compromised.
2. The ice cube tip
Empty a few ice cubes from your ice tray into a zip-lock bag or a plastic container and leave it in your freezer. They will hold their form as long as the freezer remains working, but if you ever find them frozen flat, you’ll know that the freezer was off long enough for them to completely melt.
