How much does it cost to charge your phone or your toothbrush? Is it really cheaper to use the microwave to cook your food, as has been suggested? With the cost of electricity putting the squeeze on all our finances, and a house full of tech, I decided it was time to see how power-hungry everyday devices really are.

We are constantly told that all manner of appliances chew through electricity, and that you can make huge savings by switching off “vampire devices” at the wall. But is that really true? To cut through the fug and find out myself, I grabbed a power meter and spent the last two months testing everything I could.

Some devices get a bad rap for a good reason, guzzling electricity like nobody’s business. Some older wifi routers will fall into that category, and my testing suggests you may also be paying more than you think to watch TV. I was also surprised at how much it cost to use our hairdryer. However, I found that other devices were reassuringly frugal.

Some manufacturers provide electricity consumption figures for their products. Others print the maximum amount of power a device can use in watts (W) on its plug.

Measuring the amount of electricity used yourself with a simple power meter is easy. They cost under £20, slot in between your device and the power socket and can typically measure from 0.5W and up. You may be surprised by what you find.

To convert watts into kilowatt-hours (kWh), the energy unit in which consumption is measured, simply divide by 1,000 and multiply by the number of hours in use.

Here’s the good, the bad and the ugly from my research.

The good

According to my testing, a lot of the technology made in the last five years was fairly energy efficient, drawing less than 0.5W in standby mode, so would cost a maximum of £1.50 if left plugged in all the time for a year, but likely far, far less.

That included the TV, monitor, smart kettle, smart bulbs, Xbox games console, smart hubs for the lights and thermostat, and many other devices, including various phone, tablet and laptop chargers.

However, one standout was my 10-year-old Panasonic microwave, which consumed 2W when not doing anything other than displaying the time – a £6-a-year charge I could do without.

Wirelessly connected systems typically consumed a little more. Sonos speakers, which connect via wifi to each other and the internet, drew between 1W and 3W (£3-£9 a year) when on standby, depending on age.

Smart speakers were pleasingly energy efficient. Amazon’s Echo Dot with Clock and Google’s Nest Mini consumed less than 0.5W when idle and only 2.3-4W (less than 0.13p an hour) when pumping out music at maximum volume.

LED smart bulbs were also fairly efficient, consuming about 6W (0.17p an hour) when turned up to maximum brightness, which is roughly the same as their non-smart equivalents.

Charging portable electronics is generally low-cost. Smartphones typically cost less than 1p a full charge, while an iPad Air costs about 1.4p, and a laptop, such as the 14in MacBook Pro, costs 3.4p to fully power back up. A Philips electric toothbrush costs less than 3p in electricity to use a year.

Modern set-top boxes also consume very little power. The latest Apple TV 4K and Sky’s new Stream box draw less than 0.5W in standby and cost 0.07p and 0.14p an hour respectively while watching movies. Older boxes, such as Sky Q, consume about 12W (0.4p an hour) when watching TV but go into a deep sleep overnight, drawing less than 0.5W when not recording or updating.

The bad

Generally speaking, if a device has a screen or emits light, it consumes more electricity. Google’s 7in Nest Hub draws about 2.7W (0.09p an hour) when displaying photos, costing roughly 1.5p a day to keep plugged in. Amazon’s bigger Echo Show 10 costs just under 4p a day to run.

My 28in 4K Asus computer monitor costs just over 1p an hour to use. However, my TV produced one of the biggest surprises. My mid-range 55in LG OLED TV costs 2.2p an hour to watch for HD content. Start watching HDR content or gaming, however, and the cost increases to about 3.3p an hour.

The Xbox consumes about 6p an hour when gaming, which with the TV costs less than 10p an hour – far less than a gaming PC would cost.

However, using a console such as an Xbox for streaming TV costs about 2p an hour, which could quickly add up.

Another surprise might be just how much electricity your wifi router consumes. Some older models can consume as much as 18W (£53 a year). The more modern Linksys Velop MX5300 that I use draws about 10W, costing £29.78 a year in electricity per unit, of which I have four dotted around my house. Turning off the internet to save electricity probably isn’t realistic but asking your provider for the latest, more efficient model may save you some money.

The ugly

Anything that heats or moves consumed the most power in my testing, which is almost all domestic appliances.

Cooking is expensive regardless of what you do but the oven is one of the priciest. An electric fan oven at 200C costs about 45-55p an hour to run.

My 850W microwave costs about 40p an hour to run but cooks food significantly quicker. However, a gas hob can still be cheaper to use. Heating 800g of lentil soup in 10 minutes on the smallest ring cost 0.14p compared with about 2p in the microwave.

Even tea and toast quickly adds up. My Morphy Richards two-slot toaster costs about 1p a toasting, while boiling 0.5L of room-temperature water costs about 2p. However, I can save about 30% of the electricity by heating the water to only 85C for coffee using a smart kettle.

Doing the washing is fairly costly, too. A 72-minute 40C daily wash cycle in a 7kg Samsung washing machine costs 25p in electricity but significantly more at higher temperatures or longer cycles with more spins.

One surprisingly expensive item was the hairdryer. A Parlux 2200W dryer costs about 6p to use for 10 minutes.

Electric heaters are also expensive to run. Even a relatively efficient Dyson fan heater costs 16p an hour to keep a small room at 20C when the ambient temperature is 14C, which is about 5p more than the amount of gas burned an hour by my 2013 combi boiler heating the whole house under similar conditions.