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Has someone in your life ever yelled at you for leaving the lights on? Despite the shift to LED lights, it's still a good idea to turn things off because, while one light might only cost about a dollar a month to run 24/7/365 (here, I'm assuming it's a 6-watt bulb and your electricity costs $0.20 per kWh), think about how many light bulbs you have at home. It soon adds up.

Also: How I cut my power bill with IFTTT automation - in 4 simple steps

But sometimes, something that you leave on might draw a lot more power than you think, and if it's a pain to turn on and off, or if it looks like it's not doing much when it's in standby mode, people are going to be tempted to leave it on.

Something like a big coffee machine in a café, perhaps.

Small but powerful

What you need is a SwitchBot Relay 1PM switch. This is a palm-sized Bluetooth- and Wi-Fi-controlled switch that you can use to automate switches and lights, and make your dumb home appliances a lot smarter. Don't let its tiny size -- it measures 1.6 x 1.4 x 0.6 inches and weighs just 0.9 oz -- fool you. There's a lot of cool stuff packed into this package.

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Here, you have a package that can take AC inputs from 100 V to 240 V at both 50 and 60 Hz (so, essentially, it's compatible worldwide) up to 16 A. On top of this, it can handle DC power ranging from 24 V to 30 V, making it a good choice for low-power solutions.

Since no one wants to press buttons and flick switches anymore, this will integrate with several automation solutions, from Alexa, Siri, and Hey Google to IFTTT and SmartThings. It'll also work with Matter. If you've got a smart home, this SwitchBot Relay will fit right in!

The unit comes with pretty good instructions on how to fit it, but if you're in any doubt, consult an electrician, since you don't want to electrocute yourself or those around you. The unit is designed to be housed in an enclosure, like behind the faceplate of a switch or socket -- hence the small size -- and shouldn't be left in the open, since the screws on the unit are live at mains voltage and could deliver a nasty, and possibly fatal, shock. So this isn't something that you should have dangling within reach of people, kids, or pets.

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Also, bear in mind that the unit is not water-resistant in any way, so it should be treated like any other plug, socket, or switch that you have connected at home.

Perfect for home automation

The SwitchBot app offers a whole host of features.

There's the basic turning things on or off, as well as scheduling when things should be turned off and on. Beyond the basics, it can also customize what happens when the power is restored after a shutdown (do you want the switch on, off, or in whatever the last state was?), or you can have missed-touch prevention, a feature that asks you to confirm if you want the switch operated. 

This is a nice touch that prevents something important from being turned off (although I don't recommend connecting anything super critical, like a life support machine, to this switch!).

Also: I automated my home's most unexpected electronics - here are 5 ingenious results

There's also an NFC feature that allows you to pair a SwitchBot tag with the relay and control it with the touch of a phone.

Then there's power monitoring, both in the form of a live reading and historical data. This is where you get to find out how much of a power hog your devices are. There's nothing like seeing how much power something uses to make people change their ways. You can take a deep dive into usage and, if you're like me, export the data so you can number-crunch it with your favorite spreadsheet app.

Wasting a lot of power

Which brings me back to the coffee machine, a La Spaziale S5, a beast of a machine that can pull some 4,500 W of power at full load. Over a working day, this can easily be 20 kWh of power.

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That's a lot, but it's working, and it's being paid to work.

But what about when it's on standby? The owners had assumed that because it wasn't having to do much, it wouldn't draw much. I wasn't so sure. I suspected that this was pulling a significant amount over the 16 or so hours that it was on but wasn't working.

I happened to have a few SwitchBot Relay 1PM switches on hand, so I pulled the coffee machine away from the wall a few inches, squeezed my head and arms in enough to be able to wire the relay into the wiring, connected it to the Wi-Fi network, and left it for a few days (making sure no one turned it off for the test!).

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Oooooh boyyyyyy, did this thing consume power. I number-crunched the data I'd collected over a few days, and it was horrific. The S5 was burning through a whopping 8 kWh during that downtime, some 0.5 kW every hour. That didn't seem right to me, so I checked and retested it, and got the same figure. Electricity prices in the UK are dearer than in the US, and business tariffs are more so, so this equated to over $1,500 a year being wasted.

This number bothered me so much that I had to take a look at the coffee machine. These things aren't my wheelhouse, but I was convinced that there was something wrong with it. 

And there was -- there was a small water leak in the low-pressure side of the machine. Not big enough to leave a puddle (the machine is warm, so it evaporated fast), but it meant that the water tank was continuously being filled with cold water. This meant that the machine was always working. Fixing this dropped the standby power down to under 0.25 kW per hour during standby.

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That's a massive saving, even if the machine isn't turned off!

ZDNET's buying advice

Now, I'm not suggesting that most people have something that's as power-heavy as this, but at only $15, it doesn't take much savings for a SwitchBot Relay to pay for itself in a year or so. 

The truth is that you're probably going to buy more than one switch, as well as a whole raft of other smart gadgets (after all, who doesn't need at least one FingerBot?), so consider this your first purchase in what will be a slippery slope of home automation addiction.