I have been testing three of these devices, the Power Monitor from Black & Decker Corp., the very similar PowerCost Monitor from Blue Line Innovations Inc., and the more-sophisticated The Energy Detective 5000 from Energy Inc. In my tests, the Black & Decker model provided the most effortless electricity-tracking service. At $99.99, it is also the least expensive.

The devices provide real-time data about how much power you’re using across the house in terms that are easy to comprehend: cost per hour and cost per month. Turn on the microwave and watch the cost jump from 10 cents to 25 cents an hour. Turn off some lights and see the cost drop a few cents.

The Power Monitor

The firms say their customers have, over time, seen drops of as much as 20% in power bills by being more mindful of electricity use and making informed purchases, such as installing efficient light bulbs. The largest drops are often recorded in households that have (power-hogging) electric water heaters, and where the whole family gets involved in monitoring use. An independent Oxford University study in 2006 found that people getting direct feedback on their power consumption reduced use 5% to 15%.

After I began monitoring, my most-recent electricity bill dropped $10 from the month before—but that could also be due to my living in a city where air conditioning isn’t a summer necessity. I find myself thinking more about electricity, and even running back into the house to make sure the lights are out.

The monitors sold by Blue Line and Black & Decker are almost identical, because they’re both manufactured by Canada-based Blue Line. The Blue Line model costs $109, is a bit larger, and features a slightly longer range for the wireless signal that transmits power use from your electric meter.

Connecting these two devices to my electric meter was simple. First, loop a metal belt around the glass dome covering the meter. Then align a sensor attached to the belt on top of the glass to read the data collected by your meter. On my old-style meter, the Power Monitor’s sensor keeps track of how fast a dial rotates. The companies say their products work with about 90% of meters in North America. On a newer meter, the sensor would read a digital port on the front

The sensor you attach to the electric meter wirelessly sends raw data to a digital monitor that is kept inside the house. Before using the monitor, you have to enter data from your electric bill, but finding the right data can be tricky. Black & Decker’s instructions on this are relatively clear, and entering the data into the digital monitor involves a process similar to setting an alarm clock.

The digital monitors, about the size of a large remote control, can sit in one room or travel about the house. A button labeled “tare” on the Black & Decker model helps you calculate how much electricity is being used by any single appliance that you can turn off and on. Press the button and it zeros out the reading.Turn on an appliance and the device calculates its usage alone. I found surprises: My LCD TV uses just $0.02 an hour, while an electric water kettle uses more than $0.20 an hour.

The Black & Decker model features a rudimentary display that only reports the aggregate power use for your house at any given time. It can’t go back and show you changes over time.

But the latest model from The Energy Detective, known as TED, connects directly to a house’s power supply for a more-precise read than the Black & Decker. It comes with software that graphs how use patterns change over time. The TED 5000 costs $199.

But installing TED requires turning off your home’s main power line and inserting a sensor into your circuit breaker—a process that the company says should be done “by qualified personnel only.” I sought help from a friend who has a lot of wiring experience, but after several hours, we were unable to make TED work. My issue was likely a decades-old circuit breaker. The company said my configuration is atypical and that problems like this are rare. A colleague has been using TED for several weeks after hiring an electrician to install it.

While TED 5000 offers many more advanced tools for sleuthing your home’s electricity waste than the other models, all of its sophistication won’t necessarily help the average user do much of a better job remembering to turn off the lights. For most of us, the large cost-an-hour sign on the Black & Decker Power Monitor offers the only feedback we really need.

If you’re just looking to target power-hogging appliances in your house, there are even less expensive solutions. For example, the $24.99 Kill-a-Watt, which I haven’t tested, sits between one appliance and the outlet, and tells you exactly how much power that appliance is using.

And before buying any of these devices, keep in mind that many utility companies are installing a new generation of so-called “smart” meters, which not only measure real-time power use, but also offer two-way communication with the power company to help cut costs. Some will also offer software to help you monitor your power use, and Google Inc.’s nonprofit foundation is already working with power companies on a free service that connects data about your power use into an online widget. Appliance makers are also working on products that can communicate with a central controller to turn themselves up or down, on or off, according to changing prices or conditions.

All three of the monitors I tested should continue to work with most new power meters. While these devices seem downright rudimentary compared to what’s on the horizon, they certainly suffice in the meanwhile to make electricity use more visible.

Walt Mossberg is on vacation.

Write to
Geoffrey A. Fowler at geoffrey.fowler@wsj.com

According to the Daily Mail, she said: “We know how small babies need constant reassurance that they exist….My fear is that these technologies are infantilising the brain into the state of small children who are attracted by buzzing noises and bright lights, who have a small attention span and who live for the moment.”

On Feb. 12, Ms. Greenfield–a member of Britain’s House of Lords who holds the title of Baroness–said that social-networking sites like Facebook might create short attention spans.

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This past Saturday night, BoomTown attended the tony San Francisco book party for Jonathan Zittrain’s new book, “The Future of the Internet–And How to Stop It.”

It was hosted by megablogger Arianna Huffington and Melanie Ellison, an old friend of Zittrain’s from high school, as it turned out.

And BoomTown took our Flip video camera, of course.

For one, it was held at Ellison’s stunning Pacific Heights home, with a lot of Internet and San Francisco wattage in attendance, including Melanie’s husband, Larry Ellison, and Mayor Gavin Newsom.

By the way, Zittrain is professor of Internet governance and regulation at Oxford Internet Institute, Oxford University, and co-founder of Harvard Law School’s Berkman Center for Internet and Society.

And the book is actually not about stopping the Web–perish the thought, as what would I do with my life without my beloved Internet, which I would marry if it were legal?

Instead, according to Zittrain, my beloved Web is in deep, deep trouble!

He is justifiably worried about innovation continuing and the book is a bracing call to fix some of the Internet’s serious structural and other problems, before it collapses in a giant heap of too-tightly controlled mundanity.

I’m for that! Let Web Wackiness Worldwide (WWW!) reign!

In that spirit, here is a video of the party, in which I ask everyone the key question: What is the future of the Internet?

The video includes some book party speeches and thoughts from Craigslist’s Craig Newmark, Jim Steyer of Common Sense Media, Accel Partners’ Jim Breyer, Techdirt’s Mike Masnick, Zittrain and, of course, Huffington (and I also got her to impersonate Tracey Ullman impersonating Arianna to up the wacky quotient) .

And also three Internet clowns trying to impersonate me. Wackier still!

Here’s the video (there is an odd voice/video disconnect in the Zittrain and clown sections at the very end that I am trying to fix):