Why not just leave a brick of ice on the floor of the freezer and not in a container? If you come home to a frozen puddle, it’s safe to say you had a loss of power long enough that you should toss everything in it.
Along the lines of what Dewey Finn suggests, I’d buy a box of Popsicles and put them near the door of the freezer (its most vulnerable area). Those suckers melt in about a New York minute if the temperature goes above freezing. Get the brand name ones, the generics seem to freeze harder.
I have, inherited from a grandparent, a clock that uses flip-cards to list the hour, minute, and month and date (although it does not account for leap years). Plus, I’d hazard if your electricity was off by more than 1 day, you’d know it…
I lost power for about a day or so from the last hurricane, and I judged my freezer food was OK because hardly any of the ice had melted. I have a plastic “box” like thing I out the ice in from the trays, and there was little water at the bottom.
But, I had put a lot of containers of water in there, to freeze and keep it cold after the inevitable power loss.
DF is closest to right! Take a bottle cap and fill it with water. Put it in the freezer. After it freezes put a penny on top and replace it in the freezer. If you check later and the penny is on the bottom of the cap beneath the ice, the freezer has been off for a significant lenth of time.
Similarly (well exactly) when we’re testing out freezers at work (second hand freezers that we’re not ready to trust with thousands of dollars worth of product), or even some of our normal freezers…We fill a small container with water, freeze it and leave it in the freezer upside down. If there’s no ice in the container one day, you know the freezer stopped working at some point.