Yes. A smart plug that looks switched off still draws about 0.65 to 1.5 watts, based on owner measurements of popular TP-Link Kasa models. That’s the cost of keeping its Wi-Fi radio awake so your phone or voice assistant can turn it back on.
The bill impact is small. One plug running around the clock adds a dollar or two a year. Ten plugs add roughly $15, under 1 percent of what the average U.S. home buys from the utility.
So the useful question isn’t whether smart plugs use power when off. It’s whether the plug saves more than it burns. That depends on what you plug into it. A plug on a modern TV can lose money. A plug on a forgotten space heater can win.
Below you’ll find measured numbers for three plugs, the yearly cost math, and a simple test for when a plug pays off. If you want ideas for the whole house rather than this one question about plugs, read our guide to the best smart home ideas.
Smart Plug Power Draw at a Glance
| Smart plug | Draw when off (W) | Draw when on, nothing plugged in (W) | Yearly cost when off |
|---|---|---|---|
| TP-Link Kasa KP115 | 0.65 | 1.25 | about $0.99 |
| TP-Link Kasa HS110 | 1.45 | 2.00 | about $2.20 |
| TP-Link Kasa HS300 power strip | 0.85 (all six outlets off, three USB ports live) | 1.35 (one outlet on, LEDs on) | about $1.29 |
Readings come from an owner’s Kill A Watt P3 tests posted on the Sense community forum in 2021. Yearly cost assumes 24 hours a day at the 2025 U.S. residential average of 17.30 cents per kWh.
Why Does a Smart Plug Draw Power When It’s Off?
A smart plug draws power when off because only its relay is open. The Wi-Fi chip, the processor and the status light stay live so the plug can hear your next command. Your appliance gets nothing. The plug itself keeps running on a small trickle.
Think of it as a tiny computer wearing a wall plug. When you tap “off,” a relay inside clicks open and the lamp goes dark. The computer keeps listening.
A plain wall outlet or wall switch has nothing to listen with, so it draws nothing when off. That’s the trade you make for app control, schedules and voice commands.
Off isn’t zero, and it isn’t one fixed number either. In the same forum tests, the newer KP115 drew 0.65 watts off, less than half the older HS110 at 1.45 watts.
How Many Watts Does a Smart Plug Use When Off?
In owner measurements with a Kill A Watt P3 meter, a Kasa KP115 drew 0.65 watts when off and an HS110 drew 1.45 watts. Both are older plugs from one forum thread. Treat them as a realistic range, not a promise for the plug in your cart.
The owner who posted those readings also noted that results can shift a little with the plug’s distance from the Wi-Fi router. A weak signal makes the radio work harder.
Manufacturers don’t settle this for you. TP-Link’s Kasa KP125 spec page lists max load, Wi-Fi band and dimensions, but no standby draw. The Tapo P110M datasheet leaves it out too.
For scale, Lawrence Berkeley National Laboratory says most products draw under 0.5 watts in standby today. A smart plug sits above that line. That detail matters in the next section.
What Does a Smart Plug Cost to Leave Plugged In?
At the 2025 U.S. residential average of 17.30 cents per kilowatt-hour, a smart plug drawing 1 watt costs about $1.52 a year. The measured range of 0.65 to 1.45 watts works out to roughly $1 to $2.20. Your state’s rate will move that up or down.
Here’s the math so you can run it yourself:
Scale it up and it’s still modest. Ten plugs at 1 watt each use about 88 kWh a year, roughly $15. The average U.S. home bought 10,791 kWh in 2022, so those ten plugs are under 1 percent of that.
When Does a Smart Plug Waste More Power Than It Saves?
A smart plug wastes power when the device it controls idles below the plug’s own draw. Lawrence Berkeley National Laboratory says most products now sit under 0.5 watts in standby. A plug pulling 0.65 watts when off adds to your bill instead of cutting it.
Run the test in one line: does the device draw more in standby than the plug draws when off? If yes, the plug saves. If no, it costs.
Older equipment often clears that bar. LBNL notes that typical standby was 1 to 3 watts about twenty years ago, so an old stereo, printer or set-top box is a better candidate than a new TV.
The bigger win is often a device that’s fully on when it doesn’t need to be. In a federal study of office buildings, schedule timers cut plug-load energy by 26 percent at workstations and 50 percent in print rooms. That’s offices, not homes, but the logic carries: a device you can schedule off at night stops burning power for hours.
Two practical notes:
How to Pick a Smart Plug That Wastes Less Power
Pick the plug for the job and measure it once. The standby number matters less than whether the plug sits on a device that actually idles high. Three checks cover most of it.
Also check the Wi-Fi band. The KP125 is 2.4 GHz only, so it won’t join a 5 GHz-only network.
Smart Plug vs Power Strip vs Unplugging
For one device, a smart plug is convenient but costs about a watt to run. A power strip with a switch costs nothing in standby once you flip it off, and it covers a whole desk. Unplugging is free but easy to forget.
The U.S. Department of Energy says standby power is 5 to 10 percent of residential energy use and could cost an average household as much as $100 a year. It suggests plugging electronics into a switched strip and turning the strip off to cut that draw.
So match the tool to the setup:
Smart appliances keep Wi-Fi awake the same way plugs do, so the same watts-times-hours math applies to them. Our guide to smart cooking and cleaning gadgets is a good place to run it. For broader habits beyond plugs, see our house tech rules.
Frequently Asked Questions
Do smart plugs use electricity when turned off?
Yes. In owner measurements with a Kill A Watt P3 meter, an off Kasa KP115 drew 0.65 watts and an off HS110 drew 1.45 watts. At the 2025 U.S. average rate, that’s roughly $1 to $2.20 a year per plug.
Do smart plugs use more power than they save?
It depends on the device. A plug saves money on equipment with high standby draw or on anything you can schedule off. It loses money on devices that idle below the plug’s own draw, which Lawrence Berkeley National Laboratory says covers most products today.
Do energy-monitoring smart plugs use more power when off?
There’s no official number. TP-Link doesn’t publish standby draw for the Kasa KP125 or the Tapo P110M, both energy-monitoring models. The only measurements found are owner readings on older plugs, so the safest move is to check your own plug with a plug-in watt meter.
Is it safe to leave a smart plug plugged in all the time?
Smart plugs are built to stay plugged in, since that’s how they receive commands. Stay under the load rating printed on the plug. The Kasa KP125, for example, is rated for 15 A and 1,800 W. For space heaters, check the heater’s manual first.
Should I unplug smart plugs I’m not using?
Yes, if one has sat unused for months. It only costs a dollar or two a year, so it’s not urgent. But an idle plug saves nothing, and unplugging it or moving it to a switched power strip removes the draw.
Conclusion
The Bottom Line: Smart plugs use power when off, about 0.65 to 1.5 watts in the owner data, or roughly $1 to $2 a year each.
That’s too small to worry about for a few plugs. It’s worth a second look if you have a dozen idle ones, or if a plug sits on a modern device that idles under half a watt.
Use plugs where they earn their keep: older gear, devices you can schedule off, and things you tend to leave running. Skip them on low-standby electronics. If you’re unsure about a plug you already own, put a watt meter on it for ten minutes.
