Kill A Watt EZ
The Kill A Watt EZ power plug meter from P3 International is, at $60 list, the least expensive of the three tested here. It's also the easiest to use.
At 5 by 2.25 by 1.5 inches, the Kill A Watt EZ meter is about the size of a double-thick Palm PDA. It plugs directly into an electric outlet, which you would think was highly convenient -- but not necessarily a good location for it, however.
Although the numbers on its one-line LCD display are moderately large, the labels that also appear on the LCD (such as time, volts, cost, etc.) are small and hard to read if you don't have good eyes. In fact, if your vision is less than 20/20, you may want to connect the Kill A Watt EZ to your outlet via a short extension cord, so you can more easily see the display.
The Kill A Watt EZ has five rubberized buttons: Menu, Up, Down, Set and Reset. It has built-in battery backup , so it will retain current information when unplugged.
The device calculates cost per hour, week, month or year, easily toggling the amounts for the various time periods. The Kill A Watt EZ's kilowatt and dollar displays have only two decimal places -- so the displayed reading on a low-wattage device, if it's a subpenny reading, looks like zero.
This is rather alarming, until you realize that the Kill A Watt EZ is actually capturing the data. As a result, if you want to check your power costs on a low-power device, you're probably better off looking at the per-month or per-year values.
Kill A Watt also offers a power-strip version, the Kill A Watt PS ($99.95). With this version, you also get six regular outlets and two wide outlets. In addition, it's at the end of a 6-foot cord, making the readout possibly easier to see.
However, the Kill A Watt PS won't do the cost calculations, nor do per-outlet measurements -- you're better off plugging a power strip into the Kill A Watt EZ.
If all you're looking for is basic power usage and costs, the Kill A Watt EZ will do the trick. Just get a short, heavy-duty power cord, and remember to toggle the cost-per-period if you're seeing $0.00 as your power cost.
Watts up? Pro
Electronic Educational Devices' family of Watts up? meters includes the Standard ($96), Pro ($131), Pro ES ($196) and .Net ($236). The latter is getting out of the impulse purchase range, but the added capabilities, if you want them, can make it a bargain.
The Watts up? Standard, as the name suggests, is the basic model, capable of measuring and calculating power usage, but without fancier features like logging readings or the ability to upload logged records to your computer.
The Watts up? Pro and Watts up? Pro ES include internal EEPROM (nonvolatile) memory for logging, and a USB port allowing download captured or real-time data records, viewable as records, or report and graph displays. You can track not just a device's power usage, but also power quality. In stop/overwrite mode, the Watts up? Pro can hold up to 32,000 records of watts reading; in automatic mode, recording all parameters, it retains about 4,000 records. The Watts up? Pro ES will hold four times as many records.
The Watts up? .Net has all the features of the Watts up? Pro ES, plus several that make it especially useful for IT and for support techs, such as a built-in Web connection, Ethernet port and power relay.
I tested the Watts up? Pro. The 6-foot built-in power cord made it easy to plug the meter into an outlet and still be able to read it and hit the buttons. And unlike the Kill A Watt EZ, the Watts up? Pro displays pricing down to tenths of a cent.
With only two buttons, Mode and Select, and 18 distinct pieces of data you can choose to display and/or reset using these buttons, the Watts up? Pro is much less user-friendly or intuitive than the Kill A Watt EZ. And there's no menu, instructions or other summary on the front of the machine, just the "Select" and "Mode" button labels, so you have to remember or guess what's what and how to get to it.
There are printed instructions and a one-page reference chart summary (PDF), but these include action/item numbers that don't actually appear on the Watts up? meter or display. This led me to initially set my cost-per-kilowatt setting incorrectly, which I didn't notice until I became suspicious of the way-too-low cost/kilowatt readings.
The Watts up? Pro meter starts a fresh session every time you unplug it from the wall, and you can reset the session manually.
The Watts up? Pro very badly needs a clear, separate "session start" reset-readings-to-zero button, or a serious UI overhaul. However, with practice, and the summary sheet, it's not too hard to get the hang of using the device. Watts up? Pro includes Windows software to download and display logged data; a real-time version is available for $79. If you're not a Windows user, there are links to user-developed Mac and Linux versions online. Also available online is a (Windows-only) Logging Interval Calculator spreadsheet calculators.