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Updated: 27 Sep 2021

How we test smart plugs

We test smart plugs more rigorously than other reviewers. Read on to find out how our tests reveal the best.
Felix Wilson
Plugged in smart plug for testing

We’ve tested smart plugs of all kinds – from pricey plugs that can connect to your boiler or security system, to affordable online marketplace models.

These flexible devices can instantly make your home 'smart', but despite their apparent simplicity, there are a range of important things to consider before you buy. That's where our tests can help.

Browse all our smart plug reviews to find your perfect model.

Why our smart plug tests are different

Most free-to-view websites base their reviews on a single tester’s impressions, with scores reflecting individual preferences. They also often receive free sample products directly from manufacturers and their representatives.

We poll consumers to see what matters most to them, and factor this into our Which? score. The results we use are calculated based on rigorous, independent lab testing – leaving no room for unconscious bias. We also buy every device we test from everyday shops – just like you do. We don’t accept free samples for any of our full lab tests.

What are Which? Best Buys and Don’t Buys?

Best Buy smart plugs are the ones that excel in our tests. As of September 2021, smart plugs that score more than 87% are Best Buys, which have our full recommendation, although it’s still worth reading our reviews to check for any weaknesses that might affect you. Smart plugs that score less than 45% are Don’t Buys.

  • Best Buy smart plugs tick the most important boxes – they have a decent array of features, are compatible with a range of devices and are easy to set up and use.
  • Don’t Buy smart plugs fail to impress: they lack basic features, are tedious to use and might even cut corners on safety and digital security.

How is the Which? score calculated?

The Which? score is a percentage. This score only reflects performance in our tests – it doesn’t take price into account. We consider a range of key test questions, and give the most important things a higher weighting. This means that key features, such as whether a smart plug can set schedules, affect the final score more than other factors, such as where the on/off switch is located.

  • 35% Features
  • 35% Performance
  • 20% Ease of use
  • 10% Design

Smart plug security and privacy

Key question: Will the smart plug fend off hackers and keep my data private? 

All smart plugs go through a barrage of industry-leading tests for how they protect you from hacking attacks, and keep your data secure and private. 

We've previously investigated smart plugs and found a whole host of issues, including plugs leaking out data and potentially posing a risk to your safety. 

If our tests flag up any causes of concern - whether that may be weakness to being hacked or problems resetting the plug if you want to pass it on - we will contact the manufacturer. 

We will work with the brand to introduce a fix and use our security alert banners to keep you informed of what is going on. 

While we don't currently include security in our evaluation, for any issues that we found which aren't fixed, we are able to hold back Best Buys or even make a product an automatic Don't Buy if the risk to you is high.

Smart plug features

Key question: can it set timers and schedules?

Timers and schedules are among the biggest selling points. They let you turn on lamps and other devices to give the impression that you’re at home while you’re away. You might be surprised to see some models with only one of these functions – or neither.

Features make up 35% of our overall smart plugs score.

Key question: does it have energy monitoring?

Smart plugs with energy monitoring let you see exactly how much power your appliances are using. The best can tell you straight away in real time exactly how power-hungry your devices are, while others struggle to give any useful information.

Smart plug reliability

Key question: do voice commands work reliably with Alexa, Google Assistant and Siri?

Some smart plugs work with a wide range of devices, apps and virtual assistants, while others require additional hardware to use smart features, or are locked to their own specific apps. We test with a range of devices, virtual assistants and voices to see whether voice commands work first time. With a Best Buy, you won’t find yourself standing in the hallway repeatedly shouting at your lamp to turn off.

Reliability makes up 35% of our overall smart plugs score.

Smart plug ease of use

Key question: how easy is it to use?

Setting up a smart plug can be as easy as creating an account and entering your wi-fi details. That’s not always the case, though – we’ve encountered smart plugs with confusing and long-winded setup processes, made worse by out-of-date instructions and diagrams.

Ease of use makes up 20% of our overall smart plugs score.

Smart plug design

Key question: how well designed is it?

The biggest design flaw with smart plugs is size – some power banks are so wide that they block the socket next to them. We test every smart plug in a standard UK socket, as well as in a tightly packed extension cable, to see that they can fit comfortably with other bulky plugs.

Design makes up 10% of our overall smart plugs score.

Read more about how to buy the best smart plug.