How Does A Smart Plug Work?
We show what goes on inside a smart plug and how we use one to run the lights at the front of the house.
The short answer
A smart plug works by switching the power to whatever is plugged into it using a relay controlled over your home network. You send commands from a phone app, a voice assistant or a schedule. Most smart plugs connect straight to Wi-Fi, while systems such as Hive link their plugs through a hub that plugs into your router.
A smart plug sits between your wall socket and the appliance, acting as a remote-controlled switch. Inside there's a small relay that does the actual switching and a wireless radio that listens for instructions from your phone, a voice assistant or a schedule you've set up. The first photo on this page shows one in a chrome double socket, with the lamp or appliance plug pushed into the front of it.
Early smart plugs did little more than turn things on and off from your phone. The best smart plugs for UK sockets now add schedules, timers, energy monitoring and routines that link several devices together, and that's what makes them useful day to day.
Do Smart Plugs Need Wi-Fi?
Yes, a smart plug needs a working home network for you to control it from an app or a voice assistant. Most plugs join your Wi-Fi directly and talk to the brand's app over the internet. Others go through a hub instead. The hub plugs into your router and relays messages to every device on that system.
Hive is a good example of the hub approach. Its plugs connect through the Hive hub, the same hub that runs the Hive smart thermostat for your heating, so everything sits in one app. If you already own one brand's hub or thermostat, sticking with that brand for your plugs saves you juggling several apps.
Without a connection, most smart plugs still work as an ordinary socket using the button on the front. What you lose is remote control and, on some plugs, the schedules that rely on the app.
How Do Smart Plugs Work?
Once the plug is in the socket and connected to your network, everything else happens in the app. We use the Hive Smart Plug as our example here because it's the one running our front lights.
The first job is to give the plug a clear name, so you know which appliance it controls once you've got several on the go. Ours is called Front Lights because it powers the outdoor wall lights at the front of the house. We wanted those lights on through the evening and early morning but not burning all night, and a schedule on a smart plug does that without anyone touching a switch.
The Control tab, shown on the left, turns the plug on or off straight away from wherever you are. The Schedule tab on the right is where the plug earns its keep. We've set the lights to come on from 6am to 7am and again from 5pm to 11pm, and the app lets you set a different pattern for each day of the week.
The Actions tab covers one-off jobs, such as switching the plug on for 20 minutes and then off again. Depending on the model, you also get energy monitoring and the option to link the plug to other devices in the same app.
This short video shows how quickly the plug responds when we control it from a phone:
Want Outdoor Wall Lights You Can Control Easily? Use A Smart Plug! We've Tested Multiple Lights!
Smart Plug Ideas Around The Home
Anything with a standard UK plug and a mechanical on switch can go on a smart plug. Good uses for one include:
- Lighting: Plug-in security lights and garden lighting that come on at dusk and go off at bedtime
- Screen time: Cutting the power to a games console or TV at a set time for children
- Away from home: Checking and switching devices while you're on holiday
- Forgetful moments: Turning off hair straighteners or an iron you've left plugged in
- Summer nights: Running a fan for an hour after you go to bed
- Lived-in look: Switching lamps on and off while the house is empty
- Electric blankets: Stopping them running all night
- Restarts: Power cycling a router or an outdoor security camera that has frozen
Avoid putting high-load appliances such as electric heaters on a smart plug unless the plug's maximum rating covers them. The rating is printed on the plug and listed by the brand.
Drawbacks Of Smart Plugs
The biggest drawback is that everything leans on your home network. A plug at the far end of the house or out in the garage needs a decent signal from the router, and when the internet drops, so does remote control.
Smart plugs are also bulkier than a normal plug because of the electronics inside. Some cover the second outlet on a double socket, so check the size before you buy if space is tight. Most come in white or grey with a small light to show when they're on.
Is A Smart Plug Worth It?
For lights, fans and anything you forget to switch off, a smart plug is one of the cheapest ways to add some control to a home without any wiring. Whichever you buy, make sure it does scheduling, because that's the feature behind most of the ideas above.
If you'd rather have USB charging or a cleaner look built into the wall, our guide on how to change a plug socket walks through swapping the faceplate yourself.
Quick Questions And Answers
Do smart plugs use electricity when off?
Yes, smart plugs draw a small amount of power when switched off because the radio inside stays connected to your network, ready for the next command. The amount is small compared with the appliance it controls. Brands that offer energy monitoring show the reading in their app, so you can see exactly what the plug and the appliance use.
Can a smart plug work without the internet?
A smart plug still works as a normal socket without the internet, using the manual button on the front. Remote control from your phone stops until the connection returns. Hive says its plug keeps running its schedule when broadband drops, as long as the hub is plugged in and switched on. Other brands differ, so check the brand's details if your broadband drops out regularly.
Can you use a smart plug with an extension lead?
You can plug an extension lead into a smart plug, and everything on the lead switches on and off together. Keep the total load within the smart plug's maximum rating and don't daisy chain several leads. A smart power strip with separately controlled sockets is a tidier option if you want to switch devices on the same lead independently.
Are smart plugs safe to leave on all the time?
Smart plugs from established brands are designed to stay plugged in permanently, the same as any socket adapter. Buy from a known brand that sells UK-specific plugs, keep the load within the stated rating and avoid using one with heaters or other high-power appliances unless the plug is rated for it.
What do you use your smart plug for at home?
We use the Hive Smart Plug to run the outdoor wall lights at the front of the house. It's named Front Lights in the app, and a schedule switches the lights on from 6am to 7am and again from 5pm to 11pm. Nobody has to remember to flick a switch.
Will a smart plug block the second socket on a double socket?
Some do. The electronics make a smart plug chunkier than a standard plug, and on a double socket some models sit over the neighbouring outlet. If both outlets are in use, check the plug's dimensions against your faceplate before buying.
Is it worth sticking with one brand for smart plugs?
Yes, if you already have a hub or thermostat from one brand. Matching your plugs to it keeps everything in a single app. Hive plugs, for example, run through the same hub as the Hive smart thermostat. If you don't have a hub yet, most plugs join your Wi-Fi directly, so any well-known brand will do.
What can the Actions tab do on a smart plug?
The Actions tab in the Hive app covers one-off jobs, such as switching the plug on for 20 minutes and then off again. The Control tab turns the plug on or off straight away from wherever you are, and the Schedule tab sets a different pattern for each day of the week.
Richard has spent years renovating properties and turning them into rentals and Airbnbs. Like a lot of people he started out as a beginner, and these days there isn't much DIY he won't take on.