A typical microwave oven is in "standby mode" most of the time, but that doesn't mean it's not using energy. As is the case with many electronic devices, a microwave consumes energy when not in active use. So while it may be handy for checking the time, the wattage used to power the microwave's digital clock in standby mode is greater than the electricity used to reheat food.
Nearly any piece of equipment with an external power supply, a remote control, a continuous display (such as LEDs) or one that charges batteries, is consuming electricity all the time. Without a meter to monitor energy use, you can't know how much -- but it can add up. How many people leave a mobile phone charger plugged in for convenience? It's using energy even when not hooked up to a phone.
Alan Meier, a scientist at the Lawrence Berkeley National Laboratory in Berkeley, CA, conducted the first test on "energy vampires," as they've become known. Back in 1998, Meier's group found that standby power accounted for roughly 5% of all residential electric consumption in the U.S., amounting to "more than $3 billion in annual energy costs."
How to fend off "energy vampires":