Does StopWatt really work?

What's circulating

Ads for StopWatt, a small device you plug into a wall outlet, say it lowers your electric bill. The savings they promise vary. In August 2023, Snopes (in a fact check republished by Yahoo News) looked at online articles and listings that said Elon Musk and Tesla created StopWatt, and at ads promising homeowners 90% off their utility bill. It found that StopWatt was not created or endorsed by Musk, and that a photo of him holding the device had been doctored from a picture on Getty Images. The only words on the devices themselves, Snopes reported, were "Intelligent Energy Saver. Electricity-Saving Box. The Result Is the Best." In September 2026, a reviewer on StopWatt's Trustpilot page wrote about claims of a 40 to 50% cut.

This page checks the ads' promise, what the device does to a home's electric bill. It does not rate the company that sells it.

What VOM found

Devices like StopWatt are often described as ineffective for home use. They are marketed as a way to stabilize voltage or improve the "power factor", but a home's electric meter mainly measures and charges for "real power", in kilowatt-hours (kWh): the electricity the house actually uses. Power factor correction is a legitimate idea in industrial settings; it does not apply to most home electricity billing, and it would not change the number of kWh used or billed.

Ads for StopWatt have often been misleading, with fake endorsements. People who bought these devices often report no noticeable drop in their electric bills, and energy experts generally advise that such plug-in devices do not give homeowners meaningful energy savings. Proven ways to lower a home's electric bill include energy-efficient appliances, LED lighting and smart thermostats.

VOM does not test devices or read anyone's meter: it looks up and reads what public sources say about the promise.

Why a plug-in box does not change the bill

A home's electric meter bills for "real power": the kilowatt-hours (kWh) the house actually uses. Power Wizard, an electricity plan comparison site, puts it this way in an article updated in November 2025: "residential homes are billed only for real power (kWh), not reactive power."

Plug-in savers are advertised as a way to stabilize the electricity in the house or to improve its "power factor". In December 2009, a team including specialists at the National Institute of Standards and Technology (NIST) explained why devices of this type do not save a homeowner money. Internet ads for capacitor-type power factor correction devices, sometimes called Amp Reduction Units or KVARs, said they reduce the current drawn from the power line while still giving the appliances in the house the current they need. The current does go down, NIST said, but the power factor goes up to match, so the product of the two stays the same, with or without the device. A home's bill is proportional to that product, so the cost does not change.

A May 2026 guide from UDPOWER, a seller of portable power stations, makes the same point about the appliances themselves: "a box plugged into one outlet cannot make a refrigerator, air conditioner, dryer, water heater, or oven use dramatically less energy."

What is real

• Power factor correction is real, for some businesses. Power Wizard calls it "a legitimate concept used in industrial facilities to reduce waste", and UDPOWER says it "can matter for some commercial or industrial accounts, but it normally does not cut a typical residential kWh bill."
• The current from the line can go down. NIST noted that with such a device installed, the utility supplies less current to the house, so less power is lost to resistance on the way from the local transformer. The homeowner's bill, it found, stays the same. Power Wizard adds that these boxes "don't lower your real power usage or utility bill."
• A bill comes down when the house uses fewer kWh. Real savings, UDPOWER's guide says, "come from using fewer kWh, using efficient appliances, and reducing heating/cooling demand."

What to do

• Before you pay for a device that promises savings, remember what your meter counts: kilowatt-hours.
• To lower the bill, use fewer of them. APG&E, an energy supplier, wrote in October 2024 that switching to LED bulbs can reduce the energy used for lighting by 75%, and that households with smart thermostats can save up to 10% a year on heating and cooling.
• To check a savings claim on your own bills, compare the kWh, not the dollar total, and compare the same month a year apart: heating and cooling change how much a house uses from one month to the next.
• Saw an ad for StopWatt or another plug-in saver? Paste its text into VOM before you buy.

Frequently asked questions

Does StopWatt really work to lower your electric bill?

Not according to the sources VOM read. A home is billed for the kilowatt-hours it uses, and a plug-in box of this kind does not change that number. NIST found in 2009 that power factor correction devices marketed to homeowners do reduce the current drawn from the line, but the power factor rises to match, so the bill stays the same.

What do StopWatt reviews say?

On September 29, 2026, StopWatt's Trustpilot page had 76 reviews. Its newest reviews mostly say the buyer's bill did not go down, or went up; one reviewer wrote that the device "made no difference in year-over-year electrical usage." One five-star review, by a reviewer in Texas who says they are an electrician, reports a bill of $750 one month and $330 the next, and says the current (amps) they measured became steadier. The meter bills kilowatt-hours, not amps: NIST found that even when such a device lowers the current drawn from the line, the bill stays the same. One month against the next also mixes in the weather: that reviewer wrote that temperatures had been in the 100s.

Do power saving devices really work?

It depends on what they do. Plug-in savers that promise to cut a home's bill by changing the electricity in the house do not, according to NIST and the guides above: a home pays for the kWh it uses. What lowers a bill is using fewer kWh. APG&E says switching to LED bulbs can reduce lighting energy use by 75%, and that smart thermostats can save households up to 10% a year on heating and cooling.