Slash energy costs by 30%

Kill A Watt EZ ($35, Drugstore.com) Black & Decker Power Monitor ($100, Bdonlinestore.com)

What it does: Acts as a live-in meter reader, revealing your power usage and costs. A review done at the University of Oxford says that people who monitored their usage changed consumption habits - and reduced energy bills 5% to 15%.

Plug a window AC, or any appliance, into the Kill A Watt EZ (at right), then plug that into the wall. Enter the kilowatt-hour rate from your electricity bill, and the device starts tallying costs. Or attach the Black & Decker Power Monitor to your outside electric meter. It displays whole-house usage only, but fiddling with the thermostat or lights will show you how small changes affect the big picture.

Payback time: It depends on how your usage changes. Best case: The Kill A Watt pays off in two months, the Black & Decker in five.

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