This page has been quiet, but I've made a few measurements, so I'll post 'em here.
I purchased a new Leviton GFCI (July 2018) - it has tamper-resistant flaps over the slots, and a little green LED. Leviton Model GFNL1.
I spent some time carefully measuring its power consumption. These figures are actual measurements, using calibrated Hewlett-Packard voltmeter and AC ammeter.
All measurements are at 121 volts, 60 Hz. Temp was 65 degrees F (18 C)
GFCI not tripped, no load (ie, idling with the green led on): 0.0096 amperes (9.6 ma). = 1.16 watts (rms)
GFCI tripped (ie, no output, green led is off): 0.0063 amperes (6.3 ma) = 0.76 watts (rms)
The Fairchild RV4145A integrated circuit that's the brains of most modern GFCI's needs about 1.5ma (full time). A dim LED typically eats 3 to 5 ma. This accounting leaves some 4.8ma of current unaccounted for.
So every GFCI outlet is a phantom load of about 1.16 watts, all day and night.
When my kids were little, I went around our house and installed GFCIs everywhere. Result? My 2 bedroom home has 23 GFCI outlets! That's 26.7 watts, full-time phantom load.
There's 8,760 hours in a year so that 26.7 watt phantom load turns into 234 KiloWatt-Hours of energy used each year.
In the Bay Area, Pacific Gas & Electric charges around twenty cents per kilowatt hour .... so those 23 GFCI outlets cost us about $47 each year.
(A single GFCI has a power cost of about $2 per year. Amazon sells a GFCI outlet for $10 to $12. So in 5 or 6 years, the cost of the outlet equals as the cost of the electricity it's used. Perhaps its time to add energy star ratings for GFCI outlets? )
Making things worse: At our home, there are many full-time loads that just idle most of the time: several internet routers/wifi modems, wired smoke alarms, computers, printers, a full time doorbell transformer, cellphone chargers. There's also a set of security cameras, a burglar alarm (with a battery charger). Two microwave ovens that chew up 9 watts of phantom power each. A solid-state sump-pump switch that needs 8 watts of power all the time. The refrigerator uses 15 watts even when its motor isn't going. Our furnace uses 12 watts all the time.
All together, including those 23 GFCI, my house shows a full time, baseline load of about 400 watts -- hey, that's $700 per year!
Moral: I'm pruning my phantom loads.
A simple switched power strip knocked the home-entertainment center phantom load to zero. Same with the computer printers. The furnace? Unplug it during the summer months. Replace old power supplies with higher efficiency Class V wallwarts.
And do I really want all my house outlets GFCI protected?