TVs, computers and other electrical products plugged in but not in use or left on standby cost the UK up to £1.3bn in electricity bills every year.
That's according to a new report on energy usage from the Energy Saving Trust, called Powering the Nation – household electricity-using habits revealed.
The report also reveals that people in the UK are watching 10 billion hours more TV than previously thought, adding £205m to electricity bills.
Environment minister Lord Taylor of Holbeach says: "As this survey shows, we are using a lot more energy than previously thought. Manufacturers need to develop more energy-effiicient electrical products and help consumers save money and the environment.
"We can all do simple things like switching off our TVs, computers and other home electronics when we're not using them and save up to £85 on electricity bills each year."
More after the break
Powering the Nation is the first study in the UK to measure and monitor electricity usage in real time in real-life situations, breaking down which electrical items are being used, when, for how long, and how much power they use.
It was conducted in conjunction with the Department for the Environment, Food and Rural Affairs (Defra) and the Department of Energy and Climate Change (DECC).
The UK Government says it is working with the European Union to ensure that Green Energy labels are displayed on all new electrical appliances for sale, providing information about the energy consumption and performance of domestic appliances.
• Do you leave your TV, computer or home entertainment system in standby when it's not being used? Let us know in the Comments box below.