A smart plug saves electricity only when the energy it prevents a connected device from using exceeds the plug’s own consumption. Remote control by itself is a convenience feature, not a saving. To decide whether a schedule helps, measure the avoidable load, the hours you can safely switch it off, and the electricity required by the controller.
This guide focuses on that net calculation. It is not a product review, and all numerical examples below are hypothetical rather than measurements of a particular smart plug.
Do smart plugs use electricity when the outlet is off?
Switching the connected outlet off is not necessarily the same as disconnecting the smart plug from the wall. A connected controller may remain powered to receive the next command. Check the exact model, hardware version and operating mode rather than assuming one standby wattage applies to every device.
Also check what the app measures. In its energy-monitoring FAQ, TP-Link states that the HS110/HS300 consumption reading excludes the devices’ own consumption. That is a model-specific warning, not a statement about every smart plug. An app showing zero load does not necessarily establish zero electricity taken from the wall.
Calculate net energy savings, including the controller
For a reasonably steady avoidable load, use:
Net kWh per day = (avoidable load watts × hours switched off − controller watt-hours per day) ÷ 1,000.
If the controller averages the same power all day, estimate its watt-hours as its average watts multiplied by 24. If its power differs between relay states, calculate each state separately. Watts describe power; kWh describes energy over time, as explained by the U.S. Energy Information Administration.
| Avoidable load | Load energy avoided/day | Controller/day | Net change/day |
|---|---|---|---|
| 0.5 W | 0.006 kWh | 0.024 kWh | 0.018 kWh more used |
| 2 W | 0.024 kWh | 0.024 kWh | No net reduction |
| 10 W | 0.120 kWh | 0.024 kWh | 0.096 kWh saved |
These inputs are not typical wattages or promised results. In the last example, 30 identical days would save 2.88 kWh. At an assumed $0.20 per kWh, the usage-related difference is about $0.58 per month. Fixed charges remain. Use your applicable marginal rate; time-of-use rates require calculating each tariff period separately.
Find the break-even load before buying another plug
For a constant controller draw, the break-even avoidable load in watts is controller watts × 24 ÷ hours off. With the assumed 1 W controller and 12 hours off, the load must exceed 2 W for a positive energy reduction. Fewer safely avoidable hours raise that threshold.
Buying cost is a separate question. Even a positive kWh result may yield a long financial payback. A hypothetical $20 purchase divided by the approximately $0.576 monthly saving above gives about 35 months, excluding other costs and changes in operation. Manual switching or an existing device’s sleep setting may achieve the objective without a new always-powered controller.
Measure the whole setup, not just the app’s load figure
- Define the baseline. Record how the device operates without the proposed schedule. Do not count hours it already sleeps or is already switched off as new savings.
- Confirm safe compatibility. Follow both manuals, including load type, current limits, starting current and behavior after power returns. Do not use a generic plug to control heaters, compressors, pumps or other demanding loads unless the manufacturers explicitly permit that application.
- Choose appropriate metering. Where a manufacturer-approved, properly rated upstream meter can measure the complete arrangement safely, compare total wall-side kWh over representative periods. Do not improvise adapters or stacked connections that the instructions prohibit.
- Log comparable periods. Keep active use similar and record schedule changes, outages and exceptions. If only the controlled load is measured, add the controller separately and avoid double-counting when the meter already includes it.
- Check uncertainty. Small differences can fall within a meter’s resolution or measurement uncertainty. Measure longer and treat an unclear result as inconclusive rather than reporting a saving.
Our plug-in meter versus whole-home monitor guide explains which measurement method fits the question. Never open an electrical panel or modify wiring for this check; use a qualified professional for unsuitable or hard-wired loads.
When scheduling helps—and when it does not
A schedule can help a compatible optional load that genuinely remains powered unnecessarily. It may not help a low-standby device if the controller uses more energy than it avoids. It will not reduce energy merely because you replaced a manual switch with an app and kept the same operating hours.
Keep essential refrigeration, medical equipment, security and other continuous-power equipment out of a generic shutoff routine. Preserve safe shutdown procedures and required updates. If your automation depends on a network device, cutting power to that device can also prevent subsequent remote commands.
ENERGY STAR’s smart home energy management guidance describes broader monitoring and control systems. A system-level description is not proof that one plug will lower your bill. For choosing among measurement and control tools, use our home power-saving device guide.
Frequently asked questions
Does every smart plug measure energy?
No. Confirm the exact model’s monitoring feature, units and measurement boundary. Switching, scheduling and energy measurement are different capabilities.
Can smart plugs increase electricity use?
Yes, in a setup where the controller’s consumption exceeds the energy avoided. The first hypothetical table row illustrates the arithmetic; it is not a test result.
Will switching to off-peak hours save energy?
A lower tariff can reduce usage-related cost without reducing kWh. Separate an electricity-price change from an energy reduction, and do not delay an essential load merely to chase a lower price.
What should I do first?
Identify one safe, optional load and measure its baseline. Then calculate the net difference before purchasing controls. If your whole bill is unexpectedly high, start with the high-bill diagnostic checklist rather than assuming standby is the cause.
Editorial note: educational guidance, not a product test or savings guarantee. The cover is an AI-generated illustration, not a product test. No affiliate purchase link is included. Manufacturer examples apply only to the named models and documentation.
