Pocket size EMI phantom load detector.
 

I really like the idea of this electromagnetic interference detector for detecting phantom loads, sure a Kill-a-watt works well for stuff that is plugged in that you know about, but there is always stuff plugged in that people forget is even there!

Build Your Own Electromagnetic Interference (EMI) Detector - Popular Mechanics

That is pretty cool! Its just an inductive pickup. I imagine you could guess how much of a load there is based upon how loud the noise from the speaker gets. I might have to give it a shot considering how simple the setup is.