I love my P3 Kill-A-Watt power meter, so when I spotted the Kill-A-Watt power strip at CES, I immediately knew its value: Track all your earth-killing home-theater gear with a single tool. It works, but "simple" is good and bad.
At a glance, anyone who's used a $30-$40 Kill-A-Watt knows how to use this $75 power strip, and anyone with a basic understanding of the watts and volts used to power your home should have a decent grasp of what it's doing: At any instant, you can see how many watts are being drawn to light up whatever's plugged in. Tap the Watt button to see the biggest hit taken, as well as the smallest. (You can check voltage and amperage in the same way, though the results there don't tend to get too dramatic.)
The most useful reading here is the kilowatt-hour tracker. Knowing that your car can get 32 miles to the gallon—or that it's getting 24 MPG this very second—doesn't help you budget for gasoline. The kWh tracker is like a gas gauge and average MPG tracker in one: By counting kWh over time, you instantly have a number that directly relates to your electric bill. After each billing period, you just jot down the final kWh count, and reset it.
I can imagine this might come in handy in a roommate or rental situation, where disputes over who pays what could be mollified at least in part by Kill-A-Watt's hard data. A fun thing to do is multiply your kWH by your city or state's carbon emission factor. (In 2006, Washington's was 0.5 lbs. per kWh, as opposed to the national average of 1.4 lbs per kWh.) Eventually, you could win a Nobel Prize, or an Oscar (though you'd have to share it with Melissa Etheridge).
Power geeks and generally paranoid people will find some subtle tools here that justify the extra expense: There's a "Max Amps" switch that lets you set the point at which the auto-shutoff engages. When it does go into "over current mode," the red light will flash, letting you know that you've had a surge. It also has an "over load mode" that automatically cuts out at 15 Amps, as well as an EMI filter and a self-test.
I mentioned that there were some problems with this simplicity. There's no way to track a single gadget without removing all the others—and that would mess up a lot of ongoing metering. It's probably easier to plug a standalone Kill-A-Watt into the Kill-A-Watt power strip, to monitor, say, just your TV.
You can't save or export a history in any way, so you are forced to—God forbid!—actually write or type in readings manually. Once you reset the counter, there's no looking back. Obviously, it would be great for there to be a whole energy-tracking computer inside. But then what would you use to monitor its drain on society's precious fluids? [P3 International]
Automatically starts counting kWh energy usage
Easy at-a-glance read of home theater's current energy demands, plus highs and lows
Custom settings not seen on other power strips
$75 is more than you would spend on many power strips
No way to check energy draw of individual appliances
No way to store history, or set specific periods of kWh use, tied to your bills