What is an energy monitor?
Energy monitors are small devices that help you discover how much energy you're using in your home.
They show you how much money your energy consumption is costing you, and will tell you how much money you're saving once you begin to change the way you're using energy.
What's the difference between an energy monitor and smart meters and prepayment meters?
Energy monitors are not a substitute for your existing energy meter, just a complement to it. Energy monitors also shouldn't be confused with smart meters or prepayment meters.
Smart meters are a new kind of energy meter. Smart meters make sure your energy supplier can accurately monitor your gas and electricity usage remotely, so you don't need to provide meter readings, and your bills will be completely accurate.
Prepayment meters differ from normal meters because as well as showing a meter reading, they must be 'topped-up' with credit. They are often installed in homes that have fallen into debt with their energy supplier, and can help people to budget more effectively. They can be topped-up in a variety of ways, including smartcards, tokens, keys or even coins.
How much money could an energy monitor save you?
An energy monitor alone can't save you any energy - but it will make you aware of just how much energy you're using, so it's a great tool to help you change your behaviour and cut your gas and electricity bills.
According to the Energy Saving Trust you could find that your energy usage drops by between five and 15% in the first year of using an energy monitor, which could be a saving of £25 to £75 on a £500 bill.
How do energy monitors work?
A whole house energy monitor is a hand held screen that you can take anywhere in your house. The monitor communicates with a small separate unit that clips onto your electricity meter and tells you how much electricity you're using in real time.
You can buy an energy monitor for anywhere between £30 and £100, and there are a range of different makes and models to choose from.
A few energy suppliers offer them, sometimes even for free, for example E.ON, Southern Electric and British Gas's EnergySmart scheme.
A more basic alternative to an energy monitor is a plug-in monitor. This is good for working out the power consumption of individual devices.
Plug-in meters (or plug-in energy monitors) are used between a socket and the plug of the device being measured. Some plug-in meters require a battery backup, but it's preferable to choose one that doesn't, otherwise you're at risk of losing data.
Sometimes several devices can be measured together, if a multi-socket extension lead or adapter is plugged into the monitor, making it possible to measure the power consumption of a PC, its screen and other peripheral devices in total.
How accurate are energy monitors?
Some energy monitors measure apparent power, in volt-amps, rather than actual power, in watts, and apparent power tends to be higher for devices on standby and at lower power levels generally. If the monitor only measures apparent power then it will be less accurate at lower consumption levels, at under 100 watts, and particularly under about 60 watts. (When you buy electricity, you are charged for actual power usage by the kilowatt-hour (kWh), that's the equivalent of using 1000 watts for an hour).
Whole home monitors are not as good at working out the power consumption of individual devices, as you have to measure overall consumption with a device turned on, and then measure it again with it switched off, which can be problematic and not very accurate.
However, the advantage of whole home monitors is that they can cover devices which do not have plugs, such as alarm systems, immersion heaters, lighting circuits, central heating pumps and controllers, showers, cookers, and other direct wired devices (although only in total). A plug-in meter cannot measure these.
Comparing energy monitors - things to consider
Energy monitors vary considerably in terms of their features and how much they cost, so you might want to compare a few different models before you buy one. Some of the most convenient features and benefits of energy monitors include:
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a display that shows your current energy use;
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wireless connectivity, and a portable display so you can move it around your home;
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being able to look at historical data including daily, weekly and monthly usage.
How much you want to pay for an energy monitor will depend on your individual circumstances, but it's good to remember that in most cases you are likely to make your money back if you try to reduce your energy usage as a result of buying an energy monitor.