Does a Wall Charger Waste Electricity?

A lot of eco-friendly people have beaten the drum about unplugging your chargers when not in use.  Their well-meaning mantra has been stating that most wall-warts (as they are called) are simple transformers and thusly, are always converting electricity, wasting energy and money and adding to your carbon footprint.  The science was sound, so I always believed them; however, I've forgotten the other mantra of the modern age:

There are computer chips in everything these days!

Yes...indeed.  There are computer chips in your modern chargers.  Basically, most cellphones and all smartphones use chargers that have a microprocessor in them.  This allows the charger to negotiate how much power it can/should send to your device for optimum charging.  Who would have thunk?

I ran some personal tests on smartphone and tablet chargers and found that the microprocessor turns the power off when there is no device connected.  Using a Kill-A-Watt device (a great tool if you are serious about reducing electric waste with your devices), I measured electricity usage.  The Kill-A-Watt plugs into the wall and you plug things into it.  It measures the electrical use.

This first picture is of an old-fashioned wall-wart charger.  This one charges portable speakers and has a regular round pin plug:

As you can see, the old wall-wart is eating almost 7 watts...the same as an old, large Christmas light or night light.  Now, let's plug in a phone charger from my HTC One:

As you can see, the computer inside that little phone charger sees that nothing is connected, and so, draws no power.  Most modern cell phones comply with this standard.  Every micro USB charger I could find in my house also drew no power.

So, sleep well, my friends, knowing that you don't have to keep performing that annoying task of pulling it out and plugging it in everyday.  I hope I saved you 3 seconds of your life each day!