A smart plug is a small adaptor that sits between an appliance and the wall socket and lets you switch it on or off from your phone, on a schedule, or by voice. The marketing often implies the plug itself saves energy, which it does not. What saves money is what the plug lets you do: cut a wasteful standby load to zero, run something only during the hours it is needed, or move a flexible load to a cheaper time of day. Get clear on which of those you are actually achieving and you will know whether a smart plug is worth buying or just a gadget.
The short answer. Smart plugs save money in three situations: switching off devices that waste several watts on standby, scheduling a heater or charger so it runs only when wanted, and shifting a flexible load to cheaper off-peak hours on a time-of-use tariff. They do nothing for appliances that must stay on, like the fridge, and nothing for things you already switch off by hand. The plug itself draws about half a watt to a watt to stay connected, so use them where the saving clearly beats that small overhead.
What a smart plug actually does
At its simplest a smart plug is a remote-controlled switch. It connects to your home wifi, and an app turns the socket on or off, runs it to a timer, or triggers it by voice through a smart speaker. The dearer ones add energy monitoring, reporting the watts and kilowatt-hours flowing through them, which turns the plug into a measuring tool as well as a switch.
None of that reduces what an appliance draws while it is running. A lamp on a smart plug uses exactly the same power as a lamp on a normal socket. The saving comes only from the plug switching something off that would otherwise have stayed on, or moving its use to a cheaper hour. Keep that in mind and the question stops being do smart plugs save energy and becomes what will I switch off or reschedule with one, which is the question that actually has a money answer.
Cutting standby waste
The clearest win is killing standby power on devices that draw a meaningful amount around the clock. A games console in instant-on mode, an old set-top box, a desktop in sleep, or a cluster of chargers and adaptors can each pull several watts every hour of the year. A smart plug on a schedule that cuts the lot overnight, or whenever you are out, removes that draw entirely.
| Standby load removed | Cost saved per year |
|---|---|
| 1 W | £2 |
| 3 W | £7 |
| 8 W | £18 |
| 15 W | £34 |
At 26.11p/kWh electricity, Ofgem cap July to September 2026. A constant 1 W costs about £2.29 a year.
The catch is that standby loads are wildly uneven. A modern television sips a fraction of a watt on standby, so a plug on it saves almost nothing, while a games console can waste ten times that. This is where measurement matters. Before you put a device on a smart plug, find out what it actually draws when idle, either with a monitoring smart plug or a separate plug-in energy monitor. The full story on standby power explains why some devices are worth the bother and many are not.
Scheduling things that need not run all day
The second win is using the timer to run something only during the hours it earns its keep. Plenty of appliances get left on far longer than needed simply because switching them off is a faff. A smart plug makes the off automatic.
- An electric towel rail set to two hours around shower time instead of all day. A 150W rail left on around the clock costs about £34 a year; cut to two hours a day it is under £3.
- A heated airer or dehumidifier on a fixed run rather than left going overnight by accident.
- A phone or tablet charger that you want active for a couple of hours, not plugged in drawing a trickle indefinitely.
- A water feature, aquarium accessory or seasonal lighting that has no business running while you sleep.
The saving here is not from the plug but from the discipline it enforces. If you already switch these off reliably by hand, the plug adds nothing. If you forget, which most of us do, it pays for itself by removing the forgetting.
Shifting load to cheaper hours
If you are on a time-of-use tariff with a cheap overnight rate, a smart plug can move a flexible load into the cheap window automatically. Charging a battery device, running a dehumidifier, or topping up anything that does not care when it happens during the small hours can cost less than half what it would at the daytime rate.
For this to be worth it you need two things: a tariff with a genuine price gap between peak and off-peak, and a load that can be shifted without spoiling anything. You would not move the fridge, but a charge cycle or a load that simply needs to be finished by morning is ideal. The guide to time-of-use tariffs covers how the rates work and whether one suits your pattern. Without such a tariff, shifting the hour of use saves nothing, because every hour costs the same.
Where smart plugs do not help
Plenty of plug ideas sound clever and save nothing, so it is worth being blunt about the dead ends.
- The fridge and freezer. These must run to keep food safe, and cycling them off causes spoilage and extra work for the compressor when they restart. Never put cold appliances on a switching schedule.
- Anything already on standby at under a watt. A modern TV, most modern chargers and many small electronics waste so little idle that the plug's own consumption rivals the saving.
- High-power, hard-wired or heavy loads. A smart plug is rated for a normal 13 amp socket, up to about 3kW. Do not use one on an electric heater near that limit for long stretches, and never on appliances that should keep their own safety controls, such as a heater with a tip-over cut-out you would be bypassing.
- Things you would switch off anyway. If you already turn the lamp off when you leave the room, automating it changes nothing.
There is also the plug's own draw. Each smart plug uses roughly half a watt to a watt to keep its wifi alive, costing a pound or two a year. On a device that wastes ten or twenty watts idle, that overhead is trivial. On a device that wastes almost nothing, the plug can cost more than it saves.
A worked example of payback
Suppose you measure the cluster around the television, an older games console and a recorder, and find it draws 12 watts even when everything looks off. A smart plug on a schedule that cuts the cluster from midnight to noon, twelve hours a day, removes about half that annual idle waste. Twelve watts around the clock costs roughly £27 a year; switching it off for half the day saves about £13. Subtract the plug's own watt of draw, a couple of pounds, and you net around £11 a year. A smart plug bought for under a tenner therefore pays for itself inside a year and keeps saving after that. Run the same sum for your own devices once you know their idle draw, using the running cost calculator, and the worthwhile plugs separate themselves from the pointless ones.
Choosing and using them well
A few practical pointers if you decide they suit you. Buy a model with energy monitoring for at least one plug, so you can measure idle draws and prove a saving before committing more. Check the current rating matches what you intend to plug in, and keep heaters and other heavy loads well within it. Use schedules rather than relying on remembering to tap the app, because the automatic off is the whole value. And put plugs only where you have measured a real waste, not on everything in sight, since a houseful of plugs each drawing a watt is its own small drain. Used with judgement on the right devices, a smart plug is a cheap way to stop money leaking out of standby and idle hours. For the broader sweep of low-cost fixes that pay back fast, the quick wins under a tenner guide rounds them up, and the always-on devices guide shows which household boxes are worth taming.