What's the use of putting two coins in the refrigerator?

When we decide to leave home for a while, we need to pay more attention to electrical furniture. For example, the refrigerator is very important. It is said that as long as we put a coin in the refrigerator, we can ensure whether the food in the refrigerator can still be eaten after we go home. At this time, just put a "frozen water cup" in the freezer and put a coin on it! If you come home and find that "the coin is on the top of the cup, which means there was no power failure during this period", but if "the coin ran to the middle of the cup, which means there was a short power failure during this period" (because of the short power failure, the coin sank because the water in the cup melted), then if "the coin has sunk to the bottom of the cup, which means there was a long power failure".