I just need some convincing before I start unplugging everything. I kind of assumed that USB type computer, phone, or printer chargers would use electricity. And obviously my computer, sound system, and modem/router do. I can't imagine the lamps, toaster, TV or coffee grinder would use electricity, though. Those are just some examples, but I am ready to move on from assumptions.

What should I consider unplugging?

  • 8
    I highly suggest buying a Kill-a-Watt ( amazon.com/s/… ) type device which measure how much energy is used on an outlet. Test each appliance, and see which one is really sucking energy in your home and requires unplugging.
    – Max
    Jan 25, 2014 at 1:55

5 Answers 5


You are broadly correct.

We can divide appliances into three broad categories:

  1. Items that run off external low-voltage power supplies: Examples might include laptops (when connected to mains power), printers, etc. These devices depend upon external power supplies (nowadays usually switch-mode power supplies) to convert mains-voltage AC current to DC at the correct voltage for the device. Even when the appliance is turned off the power supply itself is still powered, and so a small amount of electricity is used by the internal electronics. This applies to USB adapters as well.

  2. Items with low-voltage electronics that have internal power supplies: Examples include many things in today's home, from computers and televisions to alarm clocks and radios. This category of equipment can go either way: If you turn it off using a physical switch that isolates the power supply from the mains, then it will not draw any power when off. If you turn it off using a "soft" button that interacts with the electronics, then some power will still be required by the electronics to monitor that button for when you turn it on again. Anything with a "standby" mode falls into this category, as does anything that can turn itself on at a particular time and anything that can be activated by a remote control.

    Many PCs draw a substantial amount of power (sometimes up to ~15W) to not only monitor their power button but to allow wake-on-LAN, wake-on-keyboard, wake at a specified time, etc. Some computers have both a soft power button on the front, and a "hard" power switch on the rear. In this case, turning off the rear power switch will usually mean that no power is drawn while off, at the expense of disabling all the auto-on features just mentioned. Some televisions work in a similar fashion with "soft" off by the remote control, and "hard" off by a physical power button or switch - but some use a soft off either way.

  3. Items that run directly off mains power: A simple example is a toaster: it works by passing mains current through wires to heat them; when it is off, the circuit is broken and no power is used. Equally with most bedside lamps - there is no power supply, internal or external; the bulb is connected straight to the mains and the switch that you use physically breaks the circuit, meaning that no power is used. With more complex appliances, such as washing machines, the same complication as with the low-voltage items can apply: it is not always obvious whether you are physically breaking the circuit when you turn it off, or whether you are merely instructing some electronics to turn off the lights on the front panel. Once again one can often make a good guess from the design of the switch: a "hard" off switch must physically break the electrical circuit and will thus usually have a more defined mechanical action than one that does not.

  • The points about "soft" switches (small-travel push bottons, normally) is good, and also if it has any display it's going to use power. Our washing machine uses ~10W/12VA when "off", but our microwave uses 5W/50VA. The latter is especially bad when running off PV/inverter because it has to put out the full 50VA, on grid electricity you'll usually only pay for the 5W.
    – Móż
    Jan 24, 2014 at 22:58
  • 1
    @Ӎσᶎ youch - that's a horrendous power factor!
    – Flyto
    Jan 25, 2014 at 8:47
  • I'm almost tempted to open it up just to see how they manage to get it that bad. Scary thing is that my cheap plug-in power meter pretty much agrees with the scope and proper meter, which is almost unheard of (the cheap ones are usually +/- 2mA, or 5W at 240V).
    – Móż
    Jan 25, 2014 at 9:07
  • Great post... Anything that doesn't really have complex circuits will not use that much electricity (if any) when plugged in.
    – Blue_Hat
    Mar 23, 2014 at 16:23

I highly suggest buying a Kill-a-Watt type device which measure how much energy is used on an outlet. Test each appliance separately, and see which one is really sucking energy in your home and requires unplugging. It's the fastest and easiest solution to test precisely the devices you use.

(Note: This is a repeat of my comment, but I'm not getting any reputation for the votes up)

  • 2
    Note that the cheap meters are usually only accurate to the nearest 5W, and frequently even less if the power factor is poor. Unfortunately poor power factor is common with the "off" state of appliances. I've seen 1W/1.2VA devices read 10W or 12W on a cheap power meter, and also 10W/25VA read 5W. The ATA in Australia (www.ata.org.au) tested a few of them and concluded that for loads under 20W the meters are effectively useless. They bought a much more expensive one to rent out to members, but it's ~$200 so you'll never make that money back buying it by yourself.
    – Móż
    Jan 31, 2014 at 11:32
  • Interesting. And I'm guessing it's not like for scale, they don't give you a "precision factor" on the box? (e.g. for a scale, "5kg X 1g", maximum 5kg, and precision of 1g)
    – Max
    Jan 31, 2014 at 15:58
  • 1
    That's right. If you're really lucky it will have a specifications page in the manual that says "current 10A/0.1%" or something, but it's up to you to work out that that means 10A to 0.1% = +/-10mA, or +/- 25W for a 240V device. The one I have has a 4 page "manual" that barely covers the device name and the button descriptions.
    – Móż
    Jan 31, 2014 at 22:02

Instead of buying Kill-a-Watt type device, I advise to share it with your neighbours since you do not need it all the time - you measure how much everything consumes in different modes of use only once and then keep results in mind. You better share the power meter with the others than support the capitalism.

But simplest method to measure the energy is with your hands. The power is lost when it is translated into the heat! The devices that produce heat consume more. That is why you can be sure that "sleep" and power-off your PC makes no difference. Just put a hand on the device and it is safe if it is cold. Use Kill-a-Watt-like power meter to check that I am right.

But one thing bothers me. There are different modes of load (power factor) and it may happen that though there is no effective load (and Kill-a-Watt indicates 0), the electrical grid (or some types of electricity meter) are severely loaded. My father says that our summer house is inhabitable during winter but electricity meter counts 1 KWh in month and blames the switching power supplies. I am not sure. I would make this a question.

  • 4
    There is probably a good question about switch-mode power supplies and power factor - I suggest that you ask it :-) I agree about "does this get warm" to a degree, but it's not reliable. A small plastic object that gets warm is probably using more energy than a small plastic object that doesn't get warm, but you can't compare that something much bigger or of a different material. A warm plastic adapter is probably using a few hundred milliwatts at most, while my cool-to-the-touch computer on standby uses up to 15W (measured).
    – Flyto
    Jan 28, 2014 at 17:02
  • 6
    +1 I totally agree with sharing the measuring device with your friends/neighbors. It's a wonderful teaching tool.
    – Max
    Jan 28, 2014 at 17:45
  • 1
    Or better, find a local group that has one - many councils in Australia have them for loan/rental to residents, and there are likely hobbyist groups that do too (or have members who will lend you one). For "what does this device do" you only need the meter for 20 seconds per device, where those things are normally designed to log usage over long periods.
    – Móż
    Jan 31, 2014 at 11:34

1) Is it warm? If it generates heat it draws power, so you should consider anything that is warm as a potential energy eater.

2) Auto-shutdown your computer. This works for MOST people. You can create a scheduled task that performs a shutdown of the computer at a specific time. Task scheduler has an option to not execute if the computer is in use as well, in case you're up late. Yes, there some people who this would be incompatible with, but for most it works fine. Most computers have a "wake up" function in the bios, so the computer can automagically come on later if needed. Of course, if it can wake itself up then it too is drawing some small amount of power from somewhere to pull that off, possibly the RTC battery. The command for task scheduler to use is "shutdown.exe /s". *nix systems have essentially the same command, but if I have to explain cron to you then you don't need to be messing with it :).

3) My understanding is that Satellite dish boxes are big power eaters, as are many HDTV set-top boxes, and game consoles. I don't do this, but perhaps a lamp timer to remove power an hour or two after normal bed time and cut back on around the time you'd normally watch TV?

4) Water heaters are notorious energy eaters. I have mine on a timer, it comes on about an hour before wake-up, cuts off about an hour after I leave the house for work, and cuts back on near the end of the day for a few hours to allow for laundry, end of day showers, etc. The good part is the water stays hot for a while, so you can still get some hot water even after the timer has cut off. Most have an over-ride button in case you need it on at odd times.

  • 1
    Hi, welcome to the site! This could be a good answer for a different question... but only part 1) seems to relate to what was asked? ;-)
    – Flyto
    Mar 24, 2014 at 10:30

current flow, in the case of AC (in 2 directions ergo, alternating current AC) is the determinate as to whether there is consumption.If a lamp is plugged into a wall socket and the bulb is dark there is no consumption. If a plug in transformer (AC to DC) is plugged in but the device to be charged is not connected (like your cell phone)there is no consumption.

  • 1
    Welcome to Sustainable Living! I'm no expert on this, but I've read on multiple occasions that all transformers consume a little bit of power when plugged into a wall socket, even if no device is connected.
    – THelper
    Sep 28, 2016 at 19:18
  • 1
    The transformer case is simply wrong. Please explain how people who measure those losses are wrong. You have an impedance connected across an AC supply, so it will conduct current. You can argue that it is a small current, but you have not done that, you have stated that it is zero. I think you need much more detail in that answer, and a justification for the zero answer (either show that Ohm's Law is wrong, or that the impedance of the transformer primary coil becomes infinite when there is no load on the secondary and that in that situation there are no losses inside the transformer).
    – Móż
    Sep 29, 2016 at 0:59

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