Consumer reports reviews 2 watt measuring devices.
Both devices are sold only online. Kill A Watt costs $25; Watts Up, about $96.
We used both watt meters to measure the electricity consumed daily by a refrigerator and a computer and compared their readouts with those from a calibrated watt meter in our labs.
Guess watt? Kill A Watt and Watts Up were accurate, and both can teach you how much an appliance contributes to utility costs. If that makes you use the appliance less or at lower-cost times of day (ask your utility when those are), you could save money. The devices can also help you compare energy costs of an appliance you own now with projected costs listed on any new one you might buy.