Home Energy Audit for Kids: Hunt Phantom Power

Your house is using electricity right now for things nobody is using. Lawrence Berkeley National Laboratory’s Standby Power project puts the total at 5 to 10 percent of residential electricity use in a typical home. Apply that to the EIA’s figure of 10,791 kWh a year for an average US residential customer and you get roughly 540 to 1,080 kWh of standby annually, which at the July 2026 average residential price of 18.31 cents per kWh works out to somewhere between about $99 and $198 a year for devices doing nothing. This home energy audit for kids finds out which of your devices are responsible, and it works with or without buying a meter.

Key Takeaways

• You will measure the standby draw of ten or more switched-off devices in watts, then convert to kilowatt-hours and money per year.
• The concept is standby power: most electronics keep part of themselves awake to listen for a remote, hold a clock, keep a network link or charge a capacitor.
• Best for ages 9 to 15, because the whole point is the unit conversion from watts to kWh to currency.
• Without a meter you can still do this properly using your own utility meter and a stopwatch. The method is in Step 5.
• This is a measurement project, not an electrical project. Nobody opens a socket, a fuse box or a device. Ever.

What You’ll Need

Item	How much	Where to get it	If you don’t have it
Plug-in energy meter	1	Hardware shop or online, the socket-and-display kind	Use the utility-meter method in Step 5. Some libraries lend meters
Clipboard and recording sheet	1	Paper and ruler	Phone spreadsheet
Stopwatch	1	Phone	Any clock with seconds
Your last electricity bill	1	Drawer or the supplier’s app	Look up your country’s average residential price
Calculator	1	Phone	Pencil and paper, the arithmetic is easy
Torch	1	Drawer	Phone torch, for reading the utility meter
List of household devices	1	Walk around and write them down	—

Time: 20 min setup, 45–60 min measuring, 20 min maths Cost: a plug-in energy meter is the only purchase, and the project works without one Mess level: none

Do the Experiment

Step 1 — Walk the house and list every plugged-in thing

Room by room, write down everything that has a plug, including the ones nobody thinks about: the set-top box, the printer, the soundbar, the games console, the mesh wifi node, the external hard drive, the microwave clock, the electric toothbrush base, the charger plugged in with nothing attached. Predict, in writing, which three will be the worst. Do this before you measure anything.

Step 2 — Learn to use the meter on something obvious first

Plug the energy meter into the wall socket, then plug a lamp into the meter, and switch the lamp on. Read the watts. Switch the lamp off at its own switch and read again. You now understand the display and have seen the difference between on and standby on a device whose behaviour is not in doubt.

Step 3 — Measure each device with the device switched off

For every device on your list, plug the meter in, plug the device into the meter, and set the device to how it normally sits when not in use: TV off by remote, console in its usual sleep state, printer off at its own button. Wait thirty seconds for the reading to settle, then record the watts. Many meters round to 0.1 W, and several devices will show 0.0, which is itself a result.

Step 4 — Convert watts to kilowatt-hours and to money

The arithmetic is three steps. Watts × 24 × 365 ÷ 1000 gives kilowatt-hours per year. Multiply that by the price per kWh from your bill for an annual cost. So a set-top box sitting at 12 W costs 12 × 24 × 365 ÷ 1000 = 105 kWh, which at 18.31 cents is about $19 a year — from one box, doing nothing. Do this for every device and sort the list by cost.

Step 5 — If you have no meter, use the utility meter instead

This works and it is more interesting. Switch off and unplug everything you safely can, leaving only the fridge and freezer. Then read your own meter. If it has a flashing LED, find the nameplate value in “imp/kWh” — 1000 is the usual figure, meaning each flash is one watt-hour — and time the gap between flashes. Watts equals 3600 divided by the seconds between flashes, so a flash every 30 seconds means 120 W. If the display only shows kWh to two decimals, note the reading, wait 30 minutes, note it again, and multiply the difference by 2000 to get watts. Then plug groups back in one at a time and watch the number climb. The increase is that group’s standby draw.

What you should see: Most individual devices are far less impressive than the folklore suggests. The LBNL project notes that most products now draw less than 0.5 W in standby, down from a typical 1 to 3 W two decades ago. A phone charger left in the wall with no phone attached will usually read 0.0 W on a domestic meter, which quietly retires a piece of very popular advice. The real offenders are a short list: set-top boxes and recorders, games consoles left in instant-on, AV receivers and soundbars, laser printers, always-listening speakers, network equipment and external drives. Expect one or two devices to be responsible for more than half your total. On the utility-meter method, a typical whole-house baseline with everything “off” lands somewhere between 50 and 300 W, and finding out which group owns most of it takes about twenty minutes of plugging things back in.

What’s Actually Going On

A device that is “off” is usually only mostly off. Four things keep drawing. First, a remote-control receiver has to stay powered to notice the infrared pulse that tells it to wake up. Second, clocks, timers and settings memory need a trickle. Third, anything with a network connection keeps its radio and processor alive enough to respond, which is why smart speakers and set-top boxes are expensive to leave idle. Fourth, and least intuitively, many power supplies waste energy simply by being connected: a transformer-based supply magnetises its core on every mains cycle whether or not anything is drawing current downstream, and that no-load loss shows up as heat.

That last mechanism is why the advice about chargers is now mostly obsolete. Old linear adaptors with heavy iron transformers had real no-load losses, which is where the “vampire charger” story came from. Modern switched-mode supplies collapse to near-zero draw when nothing is connected, and regulations have pushed no-load power down hard. Your meter will show you this directly, and a child who predicted the charger would be the worst offender and found it reading 0.0 W has learned something about where received wisdom comes from.

Here is the part that keeps the problem alive despite all that improvement. LBNL’s own framing is that standby in typical products fell from around 1 to 3 W to about 0.5 W, but the number of products with standby capability rose so much that total household standby energy stayed roughly the same, now spread thinly across many more devices. That is a genuinely interesting systems result, and it is the reason the per-device figure and the household figure tell different stories. Your audit will reproduce it: lots of near-zero readings, a handful of large ones, and a whole-house baseline that is bigger than the sum of the devices you thought to check — because there are always more than you think, including hard-wired items you cannot unplug at all.

How to Explain It to Your Kid

Ages 5–8: Some things nap instead of sleeping

Compare it to a person pretending to be asleep with one eye open, listening for their name. The television is not really off; it is listening for the remote. Give them the job of finding every little light in the house that stays on when everything is “off”, and count them. That count is the idea, made concrete without any arithmetic.

Ages 9–12: Watts are speed, kilowatt-hours are distance

This is the conversion that matters and it is usually taught badly. A watt is a rate, like kilometres per hour. A kilowatt-hour is an amount, like kilometres travelled. A 12 W box is slow, but it never stops, and 12 W running all year is 105 kWh. Have them do that multiplication for every device and then rank them by annual cost. The ranking almost never matches their prediction.

Ages 13+: The no-load loss and the systems result

Give them the physics of a switched-mode power supply and why no-load draw is small but non-zero. Then give them the systems puzzle: per-device standby fell by roughly a factor of four, and total household standby barely changed. Ask them to express that as an equation with device count in it, and to predict what happens next as more appliances gain network radios. Then let them test the prediction with the utility-meter method, which is the only one that catches the devices they forgot.

The question to ask: “The charger with nothing plugged into it reads 0.0 watts, and the set-top box reads 12. If we unplugged every charger in the house for a year and left the box alone, roughly how much would we save, and is that a good use of our effort?”

Why Teaching This Early Pays Off

The transferable skill is unit conversion with a purpose, and specifically the distinction between a rate and a quantity. Watts against kilowatt-hours is the same confusion as speed against distance, data rate against data used, and dose rate against total dose. Children who get it in one domain tend to carry it, and electricity bills are an unusually motivating place to meet it because the answer is in money.

The concept-specific payoff is calibration. Energy advice is full of gestures that feel virtuous and achieve very little, alongside a small number of changes that genuinely matter. A child who has measured their own house knows which is which, and that is the difference between environmental guilt and environmental competence. It also sets up a real engineering idea: the system got four times better per device and did not improve overall, because the number of devices grew. That pattern recurs everywhere from fuel economy to data centres.

One caution about method, and it matters here more than in most of these projects. Kirschner, Sweller and Clark’s much-cited argument is that minimal guidance during instruction does not work, particularly in domains where a novice cannot safely or productively flounder. Household electricity is exactly such a domain. “Go and explore the house and see what you find” is the wrong instruction. The right one is a specific procedure with a specific prohibition attached, which is why the safety table below is not boilerplate.

Running a Home Energy Audit for Kids Safely: What Parents Should Know

Best age	9 to 15. Below 9 the watt-to-kilowatt-hour conversion is out of reach and the activity reduces to spotting standby lights, which is still fun but not an audit
Supervision	An adult does all plugging and unplugging, reads the utility meter, and decides what may be switched off. The child records, calculates and ranks
Real hazards	Mains electricity. A plug-in energy meter is used exactly like an appliance and nothing else is touched. Do not reach behind furniture into dusty socket clusters, do not use wet hands, and do not overload a socket by stacking adaptors to make measuring easier
Don’t	Never open a socket, plug, fuse box, consumer unit, meter cabinet or device case. Never use a multimeter on mains wiring. Never cut or splice a cord. Do not unplug a desktop computer, network-attached storage, medical equipment such as a CPAP, a fridge or freezer, an aquarium pump, a security system, a smoke alarm, a heating controller or anything with a battery that is charging. If you are not certain what something does, leave it plugged in

When It Doesn’t Work

• Everything reads 0.0 W. Your meter may have a resolution floor of around 0.5 W, in which case genuinely small loads are invisible to it. Check the specification. The utility-meter method aggregates many small loads and will find them where the plug-in meter cannot.
• The utility meter will not stand still. Something you forgot is cycling: a fridge compressor, an immersion heater, underfloor heating, a water pump, a dehumidifier. Watch for three or four minutes and you will see the pattern, then take your baseline during a quiet phase and say so in your notes.
• The numbers do not add up to the whole-house baseline. They will not, and this is the most interesting failure in the project. Hard-wired devices, doorbell transformers, extractor fans, boiler controls, smoke alarms and anything you decided not to unplug are all in the baseline and not in your list.
• A device behaves differently each time you measure it. Many modern devices have several standby states and drift between them, and some do overnight updates. Take three readings a few minutes apart and report the range.
• Your child wants to unplug everything permanently. Resist. A recorder that misses a scheduled recording, a router that has to be reconfigured or a freezer that thaws costs far more than the electricity. Target the top two or three on the ranked list with a switched power strip and leave the rest.

Take It Further

• The switched-strip experiment. Put the top three offenders on one switched power strip, measure the whole-house baseline before and after a week of switching it off at night, and convert the difference to money per year. This is the version that produces an actual household decision from your own data.
• Standby against active, for the same device. Measure a games console in standby, idle at the menu, and running a game. The ratio is usually dramatic, and it reframes the conclusion: for heavy devices, standby is a rounding error next to use. Honest framing beats a scary number.
• Compare a new device with an old one. If you can borrow an old set-top box, printer or audio amplifier, measure it alongside its modern equivalent. The per-device improvement LBNL describes becomes visible, and it pairs well with our look at the embodied energy of making things and with how solar panels actually work.

What to Watch For Over the Next 3 Months

• Week 4: They read a watt figure on a product label or in a review and immediately convert it to an annual number. That reflex is the whole return on the project.
• Month 2: They start distinguishing gestures from decisions, which often arrives as scepticism about something a teacher or an advert said. Encourage the scepticism and ask for the arithmetic.
• Month 3: They want to look at the bill, or at a smart-meter app, and find a pattern. Comparing a winter month with a summer one and asking what changed is a genuinely good question, and it connects to the surface-temperature work in the asphalt-versus-grass heat island test.

Frequently Asked Questions

Is it worth buying a plug-in energy meter just for this?

If you can borrow one, do. Some public libraries lend them. But the utility-meter method in Step 5 is free, catches devices a plug-in meter misses, and teaches a better lesson about whole-system measurement. Buy the meter only if you plan to keep auditing.

Do phone chargers really waste electricity when nothing is plugged in?

Almost none, on modern equipment. Switched-mode supplies drop to near-zero no-load draw, and your meter will usually read 0.0 W. The advice dates from the era of heavy transformer adaptors, which did have real losses. Measure it rather than taking anyone’s word for it.

Which devices are actually worth unplugging?

In most homes, set-top boxes and recorders, games consoles left in instant-on, AV receivers and soundbars, laser printers and old external drives. Measure first: in any given house, one or two devices usually account for more than half the total.

Can my child use a multimeter to measure this instead?

No. Measuring mains voltage or current with a multimeter requires contact with live conductors and is not an activity for children under any supervision arrangement. A plug-in energy meter is designed exactly for this and keeps everything inside an insulated enclosure.

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About the author

Ricky Flores is the founder of HiWave Makers and an electrical engineer with 15+ years of experience building consumer technology at Apple, Samsung, and Texas Instruments. He writes about how kids learn to build, think, and create in a tech-saturated world. Read more at hiwavemakers.com.

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Sources

1. Lawrence Berkeley National Laboratory. “Standby Power.” https://standby.lbl.gov/
2. U.S. Energy Information Administration. “How much electricity does an American home use?” FAQ. https://www.eia.gov/tools/faqs/faq.php?id=97&t=3
3. U.S. Energy Information Administration. “Average Price of Electricity to Ultimate Customers by End-Use Sector.” Electric Power Monthly, Table 5.3. https://www.eia.gov/electricity/monthly/epm_table_grapher.php?t=epmt_5_3
4. Kirschner, P. A., Sweller, J., & Clark, R. E. (2006). “Why Minimal Guidance During Instruction Does Not Work.” Educational Psychologist, 41(2), 75-86. https://doi.org/10.1207/s15326985ep4102_1
5. National Research Council. (2012). A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas. National Academies Press. https://doi.org/10.17226/13165
6. White, R., & Gunstone, R. (1992). Probing Understanding. Falmer Press. (Predict-Observe-Explain.)