I'm thinking about my laptop charger wall wart which is always plugged into the 110V at my desk but not always connected to the laptop. I was wondering if while the wall wart is just sitting there not connected to the laptop whether it is consuming any power (besides the LED). There is a transformer in there after all that is getting 60Hz AC waves through it. Given the number of chargers around the house these days got me to wondering.

 

Feel it. If it burns you then it wastes power.
If it is warm or cool then it uses almost no power if it is not powering or charging your laptop.

I leave my modem, router and TV digital converter box turned on all the time. They are warm and use about 10W. It costs me pennies per month but if every home uses 10W per month in my city then it adds up to a lot of electricity.

 

The way to be sure is to measure it using something like the Kill-a-Watt device. I measured the wall wart for my daughter's laptop computer (made by HP) and it measured 0 watts and 1 VA.

audioguru's method is good but not terribly quantitative.

I agree with audioguru's statement about these little power vampires. Because there are so many devices that consume low levels of power all the time in the typical home, they do wind up consuming a goodly amount of electricity when you multiply that consumption by a million or more...