If you care about energy efficiency, you’ve likely wondered at some point how much power each item in your home uses. Investing in an outlet monitor or two can help you answer some of these interesting question.

If your home is like most others, you’ll likely find that cooling and heating use up about 50% of the energy every month. Your water heater, washer/dryer, and lighting come next with about 13% each. All the other stuff taken together rarely exceeds 10% of your total energy usage. Of course, if you live in a condo with central heat and air, the math will look a bit different.

One interesting thing that an outlet monitor can tell you is just how much power those appliances are using even when they’re not in use. In a phenomenon known as phantom energy, it’s estimated that certain appliances can use up to 15% of their power usage while in the “Off” mode.

The way to cut off phantom energy use is to unplug things when you’re not using them, but few people want to take the time to do that. Using power strips helps, as you can easily turn off the power to a number of devices, such as your entire computer setup, or your TV/stereo/BluRay. Certain power strips can even use one device as a controller for the others, so for example, when you flip on the light in your living room, all devices are powered up with it.