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

Confused? Of course. So was I, when I checked out Hulu’s new “Desktop” app, launched today as part of the video service’s new “Labs” collection of experimental offerings.

Basically, it’s downloadable software that makes it easier than ever to watch Hulu’s shows and clips in the same way that you’d watch TV–on your sofa, remote in hand. But Hulu wants to make sure you don’t actually think it replaces TV.

Note how the company describes it: “A lean-back viewing experience for your personal computer” that will work on Macs and PCs with “standard Windows Media Center or Apple remote controls”–but not with Microsoft’s (MSFT) Windows Media Center machines or Apple’s (AAPL) AppleTV boxes. And it also isn’t designed to work with any other Web-to-TV software or boxes, like Vudu.

To spell this out: I’m writing this post from the “cave” that the All Things Digital team has set up for the D7 conference, and it’s full of gorgeous 22-inch and 30-inch Mac displays that are much nicer than anything that sits in my cramped Brooklyn apartment. Hulu is saying that they’d be A-OK with me watching Tina Fey and crew, via their service, on those monitors. But they don’t want me trying to get that show on an actual television.

Isn’t a screen a screen? Nope. Not to Hulu’s owners: GE’s (GE) NBC, News Corp.’s (NWS) Fox, and soon, Disney’s ABC (ABC). To them, it’s important to make the distinction between TV programming, which generates significant ad revenue and/or cable subscription fees, and online video, which generates very little at all. That’s why NBC CEO Jeff Zucker reiterated his opposition to Boxee, the software that makes it easy to move Web video like Hulu to TV sets.

Now all he has to do is convince tech-savvy entertainment consumers to play along. Good luck!

UPDATE: Several readers have suggested to me that Hulu and its owners aren’t as dumb as they seem, and that they do indeed intend to use Desktop eventually, as a Boxee-like product of their own–that is, they will use it to let people watch Hulu on TV. If so, that means that Jeff Zucker wasn’t being honest when he declared that “right now we’re committed to Hulu being an online experience, and that’s where our vision is today, and I think that will continue.”

But for what it’s worth, whenever I’ve talked to anyone at ABC, Fox, NBC or Hulu, all of them have been consistently mindful about not trying to disrupt the existing value chain that supports the cable and broadcast TV business–“the ecosystem” is the euphemism they prefer. So I don’t find Zucker’s comments so far-fetched.

Anyone want to weigh in? If you use your real name you can sound off in the comments below. Or you can drop me a line at  peter@allthingsd.com.

Microsoft says that, in most cases, the Vista drivers — software that makes hardware like printers or monitors operate with a PC — will work fine with Windows 7, which is the successor to Vista that is coming later this year. In some cases, where Windows 7 has features Vista lacked, such as its multi-touch screen features, new drivers will be required. Hardware manufacturers may also choose to do new Windows 7 drivers to take advantage of under-the-hood improvements in the new version. But Microsoft claims the Vista drivers will work in the vast majority of cases.

If you are running the much older Windows XP, as many folks are, and Windows 7 doesn’t automatically work with your hardware, you may need to obtain a new driver.

In my preliminary tests with a beta version of Windows 7, on two laptops, I found most internal and external hardware worked fine without installing any drivers. But there were some exceptions. For instance, on a Lenovo ThinkPad I was testing, the scroll function on the touch pad didn’t work, and I had to get help from Microsoft to make Windows 7 recognize that my HP printer was capable of automatically printing on both sides of a page. One hopes that, by the time Windows 7 ships, companies like Lenovo, HP and Microsoft will have fixed such issues.

You said that Windows 7 seems better than Vista, but in my view that’s a low bar. How does it compare to Windows XP, which most people I know are still using because they had no interest in switching to Vista?

I didn’t directly compare Windows 7 to XP, partly because I was just offering my first impressions of a beta, or test, version of the new edition of Windows, and was sizing it up against its much-maligned predecessor, Vista. However, my general sense is that Windows 7 will run as quickly and smoothly as Windows XP — especially an average user’s Windows XP installation, since these machines tend to slow down over the years unless you do a lot of techie maintenance on them.

In your Windows 7 preview column, you said upgrading from Vista would be a straightforward process, but that upgrading from XP would be “more cumbersome.” Can you elaborate?

Microsoft hasn’t released details, and may not even have finished the software needed to upgrade an XP machine to Windows 7. But it is likely to be a lengthy, multi-step process, as opposed to the simple, direct, relatively fast upgrade I performed on a Vista laptop. This could deter XP owners from upgrading, even if an upgrade would be worthwhile in the long run. But it might please the computer makers, who would like all those folks running XP to just buy new PCs with Windows 7 pre-installed.

You can find Mossberg’s Mailbox, and my other columns, online free of charge at the new All Things Digital Web site, http://walt.allthingsd.com.