A lot of electronics use up power even when they're turned off. The easy fix for this is to simply turn off your power board, but if you want to root out and identify the source, Popular Mechanics shows you how to build your own Electromagnetic Interface (EMI) detector.
According to Popular Mechanics, standby power adds as much as 10 per cent to your electric bill. Their DIY build should cost around $US42 and is pretty easy to make yourself. You only need an Arduino, a USB cable, a small speaker, a resistor, breadboard, insulated wire, a 9-volt battery and pack and a wire stripper.
When you're finished with the build you walk around the house with the Arduino and it will make a loud, fast noise when high levels of electromagnetic interference are detected. Yes, it's a bit more complex than just flipping the switch, but you'll be able to root out the true power leachers in your house. Hit up the post on Popular Mechanics for a full guide and the Arduino source code.
Build Your Own Electromagnetic Interface Detector [Popular Mechanics]