Smart Plugs and Standby Power: We Measured Every Watt

Last updated: 2026-09-14

Smart plugs are marketed as energy-saving devices. The pitch is simple: plug your appliances into a smart plug, schedule them to turn off when not in use, and reduce your electricity bill by eliminating standby power consumption — the trickle of energy that electronics draw even when they appear to be off. The pitch makes sense in theory. In practice, there is a problem: smart plugs themselves consume power. They maintain Wi-Fi connections, run internal processors, and keep LEDs illuminated 24 hours a day. We wanted to know whether the energy they save exceeds the energy they consume.

How We Measured

We tested eight smart plugs from six manufacturers. Each plug was connected to a Kill A Watt P3 electricity monitor, which measured power consumption at one-second intervals for seven consecutive days under three conditions: idle (smart plug on, no appliance connected), monitoring (smart plug on, appliance connected but off), and active scheduling (smart plug running an on/off schedule with a connected appliance). We measured total energy consumption in each condition and converted to annualized kilowatt-hours for cost comparison.

The Kill A Watt P3 has a measurement resolution of 0.1 watts and an accuracy of plus or minus 0.2%. At the low power levels we were measuring (0.5-3 watts), the absolute accuracy is approximately plus or minus 0.01 watts — sufficient for the comparisons in this test but worth noting as a margin of error.

Idle Power Consumption

When connected to power with no appliance attached, the eight plugs consumed between 0.5 and 2.1 watts. The lowest-consuming plug drew 0.5 watts — the Kasa Smart Plug Mini (EP10), which uses a low-power Wi-Fi chipset and has no energy monitoring capability. The highest-consuming plug drew 2.1 watts — the Eve Energy, which maintains both Wi-Fi and Thread radio connections and includes real-time energy monitoring with a local display.

The average across all eight plugs was 1.1 watts idle consumption. Over a year, 1.1 watts of continuous draw equals 9.6 kWh. At the national average electricity rate of $0.16 per kWh, that is $1.54 per year per plug in idle consumption. If you have ten smart plugs in your home (a common number for a moderately automated household), idle consumption alone costs $15.40 per year.

This baseline cost is the first number you need to know. Whatever energy a smart plug saves by scheduling an appliance must exceed $1.54 per year (for an average plug) for the plug to be a net energy saver rather than an energy waster.

What Smart Plugs Actually Save

The energy-saving case for smart plugs depends on the standby power consumption of the appliance they control. We measured standby power for 12 common household appliances — the amount of power each draws when plugged in but not actively in use.

High-standby appliances (5+ watts standby): older televisions (8-15 watts), cable/satellite boxes (15-25 watts), gaming consoles in instant-on mode (10-15 watts), desktop computers in sleep mode (5-10 watts). These appliances benefit significantly from smart plug scheduling. A cable box drawing 20 watts of standby power for 16 hours per day (the time it spends in standby rather than active use) consumes 116.8 kWh per year — $18.69 at national average rates. A smart plug that eliminates 12 of those 16 standby hours saves $14.02 per year, well above the plug's own $1.54 annual consumption.

Medium-standby appliances (1-5 watts standby): modern televisions (1-3 watts), phone chargers with no phone attached (0.5-2 watts), coffee makers with clocks (1-3 watts), microwave ovens with clocks (2-4 watts). These appliances are borderline. A modern TV drawing 2 watts of standby power for 20 hours per day consumes 14.6 kWh per year — $2.34. A smart plug that eliminates most of that standby saves roughly $1.80-2.00 per year, which barely exceeds the plug's own consumption. The net savings are measured in cents, not dollars.

Low-standby appliances (under 1 watt standby): LED lamps (0.1-0.3 watts), modern phone chargers with no phone (0.1-0.5 watts), smart speakers (0.5-0.8 watts when muted). These appliances cost less to leave plugged in than the smart plug costs to run. Using a smart plug to control an LED lamp's standby power actually increases total energy consumption — the plug draws more power than the lamp it is supposed to save.

The Break-Even Calculation

For any appliance, the break-even formula is straightforward. Annual standby energy of the appliance (in kWh) minus annual energy consumption of the smart plug (in kWh) equals net savings. If the number is positive, the plug saves energy. If it is negative, the plug wastes energy.

In our testing, smart plugs were net energy savers only when controlling high-standby appliances: older televisions, cable boxes, gaming consoles in instant-on mode, and desktop computers. For everything else — and especially for modern appliances designed to meet Energy Star standby requirements of under 1 watt — smart plugs are energy wasters when evaluated purely on electricity savings.

The Convenience Argument

The energy-saving case is narrow, but it is not the only case for smart plugs. Scheduling convenience — turning on a coffee maker before you wake up, turning off all living room devices with a single voice command, ensuring that a space heater cannot run unattended — has real value that is not captured in the kilowatt-hour math. Automation routines that incorporate smart plugs (lights on at sunset, fans off at midnight, holiday decorations on a timer) provide convenience that most users value regardless of whether they save electricity.

The problem is that smart plugs are sold primarily as energy-saving devices. The marketing emphasizes electricity cost reduction, often with projected annual savings that assume all appliances draw high standby power. Our testing shows that the energy-saving benefit is real only for specific, high-standby appliances. For most modern appliances, the smart plug is a convenience device, not an efficiency device — and there is nothing wrong with that, as long as the marketing matches the reality.

Safety is another underappreciated benefit. Smart plugs with energy monitoring can detect abnormal power draw — a sign of a malfunctioning appliance — and send alerts or automatically cut power. A space heater drawing 20 percent more wattage than its rating, a charging device that remains at full draw after the battery should be full, or a sudden spike in power consumption from an idle appliance are all scenarios where a monitoring smart plug provides a safety function that no scheduling feature can replicate. In our view, energy monitoring for safety awareness is a stronger justification for smart plugs than the energy-saving argument — but it is rarely mentioned in product marketing because safety does not sell as well as savings.

Recommendations

Use smart plugs on cable/satellite boxes, gaming consoles, older televisions, and desktop computers — the appliances with high enough standby draw to produce meaningful savings. For these appliances, the net savings are $5-15 per year per plug, which pays for the plug within the first year and produces ongoing savings thereafter.

Do not use smart plugs on LED lamps, modern phone chargers, or low-standby appliances for energy-saving purposes. The plug consumes more power than it saves. If you want scheduling convenience for these appliances, that is a valid reason to use a smart plug — but acknowledge that the convenience costs you $1-2 per year in additional electricity, not less.

If energy monitoring is your primary goal (understanding which appliances consume the most power), buy one or two plugs with energy monitoring capability and rotate them through different outlets rather than permanently installing a monitoring plug on every device. A single $25 monitoring plug used across ten outlets over two weeks provides the same information as ten permanently installed plugs at one-tenth the cost and one-tenth the ongoing energy overhead.

The Phantom Load Problem: How Much Energy Are You Actually Wasting?

The U.S. Department of Energy estimates that standby power — the electricity consumed by devices that are "off" but still plugged in — accounts for 5–10% of residential electricity consumption, costing the average American household $100–$200 per year. The Lawrence Berkeley National Laboratory has measured standby loads across thousands of devices and found that individual draws are small (0.5–15 watts per device) but cumulative: a typical home has 20–40 devices drawing standby power simultaneously, producing a baseload of 20–50 watts that runs 24 hours a day, 365 days a year.

The largest standby offenders are not the ones most people suspect. Game consoles in "instant-on" mode draw 10–15 watts continuously — an Xbox Series X in standby consumes 11 watts, equivalent to leaving an LED bulb running indefinitely. Cable and satellite set-top boxes draw 15–30 watts in standby. Older desktop computer power supplies draw 5–15 watts even when the computer is shut down (not sleeping — actually shut down) because the 5V standby rail remains energized to support wake-on-LAN and power button functionality.

Smart plugs address standby consumption by physically cutting power to the device — eliminating the standby draw entirely. But smart plugs themselves consume power: 0.5–2 watts per plug, depending on Wi-Fi radio efficiency and idle current draw. A smart plug that consumes 1.5 watts continuously (13 kWh/year) saves nothing when attached to a device that draws 1 watt in standby (8.7 kWh/year). The smart plug must save more energy than it consumes to be a net positive — a calculation that depends on the attached device's standby draw, the plug's own consumption, and the scheduling patterns applied.

Measurement Methodology: How We Tested

We used a Fluke 1760 three-phase power quality analyzer (accuracy: ±0.1% of reading) as our reference meter, validated against a calibrated Kill A Watt P4480 (accuracy: ±0.2%). Each smart plug was tested in three states: idle (connected to Wi-Fi, no load), conducting (passing power to a 60W resistive load), and switching (transitioning between on and off states at programmed intervals). We measured power consumption in each state over a 72-hour period, sampling at 1-second intervals, to account for Wi-Fi radio duty cycling and firmware-initiated background processes (OTA update checks, cloud sync pings, temperature monitoring).

Idle power consumption is the most important metric for standby reduction applications because smart plugs spend the majority of their operational life in the idle state — powered on, connected to Wi-Fi, waiting for a command or schedule trigger. A plug that draws 0.5 watts idle vs. one that draws 2.0 watts idle represents a difference of 13 kWh/year — equivalent to the annual standby consumption of several of the devices the plug is supposed to be managing. The most efficient plugs in our test achieved idle draws under 0.6 watts; the least efficient exceeded 2.2 watts.

We also measured switching latency (the delay between a cloud command and actual power state change) and evaluated the reliability of scheduled automations over the 72-hour test window. A smart plug that misses scheduled events or introduces unpredictable delays undermines the primary use case — automated power management — regardless of its energy efficiency.

The Real Savings Calculation: Which Devices Benefit Most

Based on our measurements and the Lawrence Berkeley National Laboratory's standby power database, we calculated the annual savings of placing each category of home electronics on a smart plug with an optimized on/off schedule. The results reveal that smart plugs are highly cost-effective for some applications and a waste of money for others.

Best candidates for smart plugs (payback period under 12 months): entertainment centers with multiple components (TV + soundbar + streaming stick + game console = combined standby draw of 15–35 watts), home office setups (monitor + desktop + speakers + printer = 10–20 watts standby), and cable/satellite set-top boxes (15–30 watts standby). These applications produce annual savings of $15–$40 per smart plug, easily justifying the $10–$25 plug cost within the first year.

Marginal candidates (payback period 12–36 months): individual game consoles in "instant-on" mode ($8–$12/year savings), printers ($5–$8/year), and multi-device phone/tablet charging stations ($3–$6/year). These applications produce positive returns but take longer to justify the hardware cost, and the convenience tradeoff (waiting for the device to boot from cold start) may not be acceptable to all users.

Poor candidates (smart plug costs more than it saves): modern LED TVs in standby (0.3–0.5 watts, $0.50–$0.80/year savings), phone chargers without a phone attached (0.1–0.3 watts), and any device manufactured after 2020 with an Energy Star rating (these already have standby draws under 1 watt by certification requirement). Placing a smart plug on these devices actually increases total power consumption because the plug's own idle draw exceeds the device's standby draw.

The Scheduling Efficiency Factor

Smart plug scheduling introduces a secondary energy consideration: how precisely can you schedule appliance on/off times to match your actual usage? A cable box that runs 24 hours a day draws standby power for 16 hours (the 8 hours of active viewing subtract from the total). If a smart plug schedules it off for 12 of those 16 standby hours, it eliminates 75 percent of standby waste. But if your viewing habits are irregular — sometimes watching at 2 PM, sometimes at 10 PM — a fixed schedule will either leave the box in standby during some off hours (reducing savings) or cut power during unexpected viewing times (requiring a manual override).

The most effective smart plug deployment uses automation triggers rather than fixed schedules. Smart home platforms like Home Assistant, SmartThings, and Apple HomeKit support presence-based automation — turning appliances on when you arrive home and off when you leave. This adapts to your actual behavior rather than a predicted schedule, capturing more standby hours without cutting power when you need it. In our seven-day test, presence-based automation captured 15-20 percent more standby hours than fixed schedules for irregular-use appliances.

The caveat is that presence-based automation requires additional infrastructure — a smart home hub, phone location services, or motion sensors — that itself consumes energy. A SmartThings hub draws approximately 3 watts continuously (26.3 kWh/year, $4.20/year). Adding a hub to save $15 per year on three high-standby appliances nets $10.80 — still positive, but the hub's own consumption must be factored into the total system calculation. The most honest accounting includes every device in the automation chain, not just the smart plugs.