Keep an ice cube in a shot glass in your freezer to detect power outages

This is useful for people who are away from home for days at a time. If there's any possibility that you could lose power for long enough for your freezer contents to spoil, keep an ice cube in a shot glass in there. Upon returning home from a trip, check to see that it's still ice cube shaped. If it has melted and refrozen into the shape of the glass, you probably should discard everything in your freezer.