New GFCI's always use electricity?

You are wrong. You have to measure the current flow in both sides of the AC supply for an imbalance. They have always used a few mA to power the detector circuit.

How hard would it be for you to test one?

There has always been an electronic circuit board drawing a very small amount of idle power. Since a few years ago, GFCIs need to continuously inject a signal on the lines to detect a N-G short, so the idle power consumption is up slightly from older models that did not. The LED is also a more recent addition which adds to the power consumption. I don't know the actual wattage, but it is extremely small to the circuitry. The LED may be the biggest consumption.

On the ones I have looked at, the circuit power comes from the line side, so it will draw idle power even when tripped. That may or may not be true on all of them.

Ben Miller

The ones with LED lights are optional, you can still get them without lights. I know I wouldn't want one in a bedroom. I like the room totally dark.