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.
3. The ice pop tip
Lay an ice pop horizontally over another object in the freezer. If it is still lying straight when you arrive home, the freezer has been working fine. If it has sagged over the edges of the other object, you’ll know the freezer has defrosted a little. If the ice pop has bent all the way down to lie flat against the sides of the other object, you’ll know it turned to liquid.