Place a “cup of water with a coin on it” in the freezer.
Fill a glass with water, freeze it, and place your coins and money in it before you leave. If there is a power outage during your trip, such as a lightning strike, and your freezer thaws and refreezes once, the coins will freeze again while submerged in the water. If the coins are at the bottom or in the middle when you return home, it is a sign that they have “melted once. It functions as a simple and reliable power failure detector that allows you to determine at a glance whether foodstuffs are at risk, which cannot be determined by appearance. Please make it a habit to protect your family from food poisoning.
