Funny story: a dad in Australia found out that his daughter was throwing a major party while he was away from home. Using an online energy monitor, he saw heavy usage on New Year's Eve when he wasn't expecting to see such a spike. He returned home the next day and found all the other evidence that one might expect to find when your teenage daughter hosts a secret party.
Moral of the story? Your home energy monitor will help you save money, and maybe even teach your kiddo a good lesson.
Source: Mother Nature Network