Energy monitors -- specifically, home power meters -- are designed to help you identify ways to cut your electricity bills by a significant amount without major changes in lifestyle. Instead, satisfied owners of home energy monitors say they've been able to lower their costs within a month of use, mainly by finding out which devices are worth unplugging between uses or putting on a timer.
You can also use a home power meter to calculate the cost of electricity used by appliances you're considering for replacement with more energy-efficient models. The monitor can show you exactly how much money you'd save in electricity, so you can calculate the payback period. Owners say this has helped them prioritize replacements.
The savings made possible by a home power monitor can be substantial. A Feb. 2011 article in The Wall Street Journal notes that, based on a survey of 36 studies by the American Council for an Energy-Efficient Economy, average savings from using a home energy monitor are 9.2 percent -- just by tracking overall usage during the month. Average savings jump to 12 percent when specific appliances and devices are monitored.
Among basic energy monitors, the Belkin Conserve Insight F7C005q Energy-Use Monitor (*Est. $30) earns kudos as the simplest way to find out how much it costs to run a device that runs on 15 amps or less. The Belkin monitor, which measures energy at the outlet level, has three simple buttons: one for real-time electricity usage in watts, another for the carbon footprint this represents and a third showing the projected monthly and annual cost.
Cost estimates are based on the electricity price (from your monthly bill) that you program into the monitor. After the Belkin energy monitor is plugged into an outlet for at least 45 minutes, the dollar projection starts to be based on average electricity used. (You have to be careful to reset the monitor if you unplug one device and want to measure usage for another one.)
Most owners reviewing the Belkin power monitor praise not only its simplicity and ease of use, but also the convenience of the 5-foot cord that lets you position the LCD display at a convenient height. This is one major advantage over the competing Kill a Watt monitors by P3 International, which position the LED display at the outlet. Monitors of both brands have relatively small displays that aren't backlit, so owners say it can be quite a strain -- often entailing a crawl on the floor with a flashlight -- to read the Kill a Watt display.
Otherwise, the P3 International P4460 Kill a Watt EZ energy monitor (*Est. $30) also draws positive feedback, and it does provide more detailed reports for the same price -- including an evaluation of the outlet and the power supply to it. The display can show line voltage, current draw, power factor, line frequency and more. Rather than a cost projection, the Kill a Watt EZ tells you actual kilowatt hours (kWh) (though you can calculate this pretty easily from the Belkin monitor too). Some owners like the greater detail the Kill a Watt EZ monitor provides, while others prefer the simplicity of the Belkin energy monitor.
Even the best plug-in monitors have some drawbacks. Unless you buy several monitors, it takes time and patience to investigate one electrical device's usage at a time. There are also other limitations. Plug-in electricity usage monitors don't work on outlets or fixtures controlled by a switch; nor do they work on large appliances that draw too much power. Also, some appliances might be plugged into outlets that are hard to reach. You'll have to keep your own records about usage and cost projections.
Whole-house energy monitors allow you to track your entire home electricity use as you go, without waiting for the monthly bill. You can also calculate how much a single large appliance (such as a clothes dryer) costs by reading the monitor's display when you turn the appliance on and off. Whole-house monitors attach a sensor and transmitter to your utility's electrical meter or, in some cases, to your circuit box. You can read usage data indoors from a tabletop display or on your computer. This is a lot more convenient than running out to read your meter when you turn a device on or off, then making all the calculations yourself.
The Black & Decker EM100B Energy Saver Series Power Monitor (*Est. $50), made by Blue Line Innovations, is the simplest type of third-party home power meter. A sensor attaches to your utility company's meter, then sends data wirelessly to a display indoors, showing real-time usage plus cumulative cost. You can also press a button when turning on a big appliance to show just the difference this makes -- a real plus.
Some owners report problems with the sensor (which fits most but not all electricity meters), or with the wireless transmission. The main drawback, though, is that the monitor only measures differences of about 100 watts. It's not sensitive enough to measure the electricity used by a small device or one in standby mode, so you'll probably still want a plug-in monitor as well.
The maximum range of the Black & Decker EM100B power monitor is 60 feet (through a single wall). If you want to use the display through more or thicker walls, this may prove frustrating. Blue Line Innovations makes a similar energy monitor with a larger display and longer wireless range; the payback period will be a lot longer, though, for the Blue Line Innovations BLI-28000 PowerCost Monitor (*Est. $110).