I have been testing three of these devices, the Power Monitor from Black & Decker Corp. (BDK), 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 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. 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.

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.

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.

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. And Google Inc.’s (GOOG) nonprofit foundation is working with power companies on a free service that connects data about your power use into an online widget.

Walt Mossberg is on vacation. Email Geoffrey A. Fowler at geoffrey.fowler@wsj.com

Wireless cellphone earpieces can make people look faintly ridiculous as they stroll down the street or around the office, seemingly talking to themselves with ugly appendages sprouting from their heads. The pulsing blue lights on these things can make people look like robots. And these battery-powered gadgets, which use a power-hungry wireless technology called Bluetooth, are just one more thing to charge.

But such headsets are becoming more necessary, at least in the car. A growing number of cities and states are requiring all calls made while driving be conducted in a “hands-free” manner. Two more big states, California and Washington, will begin enforcing such laws in July. Unless drivers in these places have cars with costly built-in Bluetooth speakers and microphones, many will turn to wireless earpieces to make calls legally.

Now, two of the most important wireless earpiece makers are bringing out new models that attempt to make their products more attractive and functional. One is a new version of the Jawbone, which has become a leader in the high-priced end of the market. The other is a new model from Plantronics (PLT), which vies with Motorola (MOT) as the top seller of wireless earpieces.

I’ve been testing both the new $130 Jawbone, and the $150 Plantronics Discovery 925, and both work well, despite some drawbacks. Each worked properly with both an inexpensive Motorola Razr phone from Verizon (VZ) and a sophisticated Apple (AAPL) iPhone from AT&T (T). But I preferred the Jawbone, because of its technology and design.

The new Jawbone, made by a closely held San Francisco company called Aliph, is 50% smaller than the original Jawbone, which I reviewed in 2006. It continues to boast the original Jawbone’s signature feature: a remarkable ability to suppress background noise and isolate the wearer’s voice.

Jawbone performs this feat by using a sensor that touches your skin lightly to identify your voice through the vibration of the bones in your face. Using this information, its microphone can more easily distinguish your voice from background noise, and accurately suppress the latter.

This feature, originally called “Noise Shield” and now theatrically renamed “Noise Assassin,” really works. When the company first showed off the original Jawbone, it made live calls standing in front of things like weed whackers and boom boxes, and then turned the bone-sensing feature on and off to show the dramatic difference.

Aliph’s new Jawbone

In my tests of the new, much smaller Jawbone, I stood a few feet from a roaring vacuum cleaner, while on a phone call. The person I was calling could barely hear me with Noise Assassin turned off, but could clearly make me out when I turned it on.

By contrast, the Plantronics Discovery failed my noise test. It was useless anywhere near the vacuum cleaner. This was obviously an extreme case, but it served as a stand-in for other loud noises likely to be encountered in real life, like large trucks, or construction gear on the streets.

The biggest flaw in the original Jawbone, in my 2006 tests, was its performance in wind, which was poor. The Jawbone did much better in my latest tests. During a Jawbone call from a car with all the windows down and the sunroof open, my voice was easy to make out, according to the person I was calling. The new Plantronics earpiece did just as well in this wind test.

Plantronics claims its headset also enhances the voice of the person you are calling, a claim Aliph doesn’t make for the Jawbone. But, while voices sounded fine on the Plantronics, I couldn’t detect any difference between the two on that score.

Both gadgets are meant to be more stylish, and both will be available in multiple colors. But, while the Jawbone is just a smaller iteration of its original slab-like form, Plantronics has done something more radical with the Discovery 925: It has tried to make it look like jewelry. The Discovery’s electronics are housed in the diamond-shaped portion of the device that goes on the ear, and the microphone sits at the end of a long, V-shaped boom that is open in the center. Plantronics says the design is suitable for both genders, but admits it is a bit more aimed at women and at fashion-conscious men.

I believe some men wouldn’t feel comfortable wearing this new Plantronics model. It’s also longer than the Jawbone. But I did find it more comfortable to wear, since it doesn’t protrude as much into the ear.

The Plantronics claims longer talk time — five hours vs. four hours for the Jawbone, but the Jawbone claims longer standby time — eight days, vs. seven days for the Plantronics. The Jawbone weighs more, at 10 grams, compared with 8 grams for the Plantronics, but neither felt heavy on my ear.

I did prefer the Plantronics’ controls over the Jawbone’s. The former uses obvious buttons, while the latter employs unmarked, hidden buttons whose location you have to learn by touch.

Both of these earpieces do the job, but if you have to choose one, I’d pick the Jawbone.

• Find all of Walt Mossberg’s columns and videos online, free, at the All Things Digital Web site, walt.allthingsd.com. Email him at mossberg@wsj.com.

Corrections & Amplifications:

The Aliph Jawbone cellphone earpiece weighs 10 grams, and the Plantronics Discovery 925 earpiece weighs 8 grams. An earlier version of this column erroneously reported the products’ weights in ounces.