Smart meters that alert consumers about which appliances are using the most electricity are changing the way homeowners think about their power bills, says MarketWatch contributor Bill Sanderson. Duke Energy is testing smart meters and power monitoring apps that can tell homeowners how much they're spending on heat, water, or electricity per day.

About half of all American residences already have smart meters, about 64 million homes as of the end of 2015.

Utility customers who monitor their power use with smart meter systems cut their electricity consumption by 2%, says the Edison Electric Institute, a utility industry group. Other smart meter applications — such as software that lowers homeowners power use during periods of high prices — can save consumers even more, EEI says.

But there are some drawbacks for consumers to having meters installed within homes:

Utility customers need to know how the smart meters might work against them, said John Howat, a senior policy analyst for the National Consumer Law Center. Howat fears the meters might enable utilities to shut power too quickly to non-paying customers. That would undermine “last knock” rules in many states that require utility workers to knock on the doors of delinquent customers about to lose their service.

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