How Smart Meters work

A Smart Meter works by measuring the electrical current flow and voltage at regular intervals and then adding this up to calculate the power used in a half-hour period. Similarly, for gas the flow is measured at regular intervals. This information can be sent to your In Home Display and to your supplier. Different communications technologies may be used in different kinds of premises for the Home Area Network to communicate with your In Home Display, and different technologies will be used in different parts of the country to allow the Wide Area Network to send data to and from the company providing the communications.

As well as measuring energy, meters are constantly monitoring their own performance and environment. For example, they will report if they have an internal memory problem and report if the terminal cover is removed. In these cases your supplier may send someone to your home after contacting you.

End to End

The information from your meter goes first into a communications hub that is usually built into the electricity meter, and then through radio waves to the communications company. In the case of the SMETS 2 meters, it is the Data and Communications Company (DCC). From there it is sent on to the various DCC Services users who have a need for the data.

House to DCC to Supplier

We will now explain each leg of the end to end journey shown in the diagram above.

Energy Customers

In your home as an energy customer, you will have a smart meter for electricity and a smart meter for gas (if you're dual fuel). Both meters communicate with a communications hub which is normally a part of the electricity meter however, it could be separate if your gas smart meter is installed first. To power the communications in the gas meter a battery is used as it would be dangerous to use mains electricity.
In addition, you will have an In Home Display which is powered though the mains and communicates with the meters through the same communications hub. In the future, more gadgets could use the communications hub, provided they have the right security credentials.

Data and Communications Company (DCC)

To minimise costs for the long term use of SMETS 2 meters the DCC went out to tender for the communications network having split the country into regions for this purpose. So depending on where you are you could have one of two companies communicating with your meter, Arqiva Limited in the north and Telefónica (better known to us as O2) in the central and southern regions.

Once received by the DCC, the data is processed by the Data Services provider, currently CGI UK Limited. Overall, the whole of DCC is facilitated by Capita plc.

DCC Service Users

From the DCC, the Smart Meter messages can be sent to various Service Users depending on the messages content. Electricity and gas suppliers and distribution network operators will all have a keen interest in the data from Smart Meters. They will use it for the following reasons:

  • Suppliers
    • Meter readings - for billing purposes
    • Half Hourly readings - for additional services or sophisticated products
    • Maintenance messages about the health of the meter - such as memory problems
    • Firmware messages - to update the software in the meter
    • Configuration messages - to set up new products
    • Pay As You Go messages - to top up PAYG credit
    • Tamper messages - to detect theft and security attacks
    • Export meter readings - to measure how much electricity your solar cells or wind turbine is passing back to the network for load management and to credit the customer, depending on the commercial arrangement.

  • Distribution Network Operators
    • Power outage messages - to know when and where outages occur
    • Meter readings - for network billing to suppliers
    • Half Hourly readings - for network load planning
    • Voltage, Current and Power Factor readings - for network operation and planning.
    • Export meter readings - for network operation and planning.

  • Other Authorised Parties
    • Meters readings - to analyse and show you your energy usage
    • Half Hourly readings - to analyse and show you your particular energy profile shape.

Energy Calculations

You may have wondered how your energy bill is calculated, especially for gas, which is more complicated. Both electricity and gas are priced in pence per kilowatt-hour (kWh), so one multiplies the kWh by the price, dividing by 100 to get from pence to pounds.

kWh × Price ÷ 100 = £

But how do meters measure the kWh used, and what are the basic calculations that the meters carry out to determine the quantity of energy used?


The meter is constantly measuring the voltage and the current passing through the meter. It multiplies voltage measured in Volts by current measured in Amps to get power measured in Watts.

Volts × Amps = Watts

The above calculation takes no account of time, so it is an instantaneous measure of power. To get a measure of energy used we need to introduce time, in the case of electricity, domestic pricing is at the hourly level, so we use time measured in hours to get kilowatt-hours or kWh.

Volts × Amps × Hours = Watt Hours

Volts × Amps × Hours ÷ 1000 = Kilowatt Hours

It is kilowatt-hours that your meter displays as Active Energy or Active Power. A kilowatt-hour is also known as a Unit. Because a Smart Meter can measure power in both directions, it may also indicate IMP or IMPORT to show the power consumed as opposed to the power exported.


A gas meter simply measures the volume of gas that passes through it. Older gas meters measure the volume in units of 100 cubic feet (ft3) and newer meters in cubic metres (m3). The suppliers systems hold the meter details and so can accurately calculate the volume of gas used.

Suppliers then have to convert the volume of gas used into kWh for billing. The following equation is used:

Volume × Metric conversion × Calorific Value × Volume Correction ÷ 3.6 = Kilowatt Hours

What do these terms mean, and why are they necessary?

The volume of gas used; measured in cubic metres or hundreds of cubic feet.
Metric Conversion
If you've got a metric meter, you can ignore this step. If your reading is in cubic feet, then a conversion factor of 2.83 must be applied to convert to cubic metres.
Calorific Value
Calorific Value (CV) describes how much heat is generated when a known volume of gas is burned. Suppliers' bills show the value of CV used, which is typically between 37.5 and 43.0 MJ/m3 (Mega Joules per metre cubed).
The CV of the gas at each Local Distribution Zone is continually measured by the National Grid who sends this figure to your gas supplier, who then uses it for their calculations.
Volume Correction
The volume correction factor is used to take into account the temperature, pressure and atmospheric conditions at a property. This factor is typically 1.02264 unless your household has unusual atmospheric conditions. You can usually find this number on your gas bill.
Joules to kWh
We have ended up with Mega Joules from the above calculations. One kWh equals 3.6 million Joules, so we finally divide by 3.6 to get the energy used in kWh.
(Page updated: 2021-06-12)

Questions & Answers

Why is my IHD (smart meter display) showing "waiting for current data"?
This means that the IHD (In Home Display) is no longer talking to the communications hub on the electricity meter. There are various steps to try to correct this:
  1. We suggest you wait 24 hours to see if the device reconnects.
  2. If not move the IHD close to the electricity meter and wait another 24 hours for reconnection.
  3. Try resetting your IHD and wait another 24 hours. There are various methods to reset an IHD depending on the model. Find a guide for your device at
  4. If this does not work then contact your energy supplier who will have to send commands to the devices to re-run the connection process.
(Updated: 2021-01-21)

Is my Smart Meter working?
Citizens Advice have developed a tool to tell you what type of smart meter you have in your home and if it's working in smart mode. The tool can also tell you if your meter should work in smart mode after switching supplier. Access the tool here: Citizens Advice Smart Meter Checker. (Updated: 2021-10-30)

What services do I have on a meter that's "gone dumb"?
On a meter that's "gone dumb" you will only retain the ability to see kWh on your IHD. As the supplier can't communicate with the meter they cannot send the details of a tariff to the meter so the p/kWh rates and £ will not be updated. Additionally no meter readings can be automatically collected. (Updated: 2020-02-09)

What does "going dumb" mean?
When a meter 'goes dumb' it means that the communications to the meter have stopped. This could be due to a communications failure or due to the current supplier not supporting the communication method to that meter. (Updated: 2018-05-12)

What is surge pricing?
Media headlines about electricity surge pricing have suggested something bad is going on - it is not. When the media use the emotive term surge pricing they are referring to the facility to price different time bands at different prices. This has been going on for decades, Economy 7 is an example.
This does not mean it will cost people more as, firstly you would have to agree to be on such a tariff, and secondly if you do not change your pattern of use it is likely to cost you the same as a simple tariff. The advantage is that if you reduce your demand at the times of high prices you will save money.
Smart meters make it easier to provide time banded rates as they can provide time bands at 30 minute intervals if required. (Updated: 2022-04-18)

I can see two model numbers on my meter, which should I use?
When looking at an electricity smart meter it can be confusing to see two model numbers. In fact the communications hub module is placed on top of the electricity meter so you can see a model number on the top for the communications hub and a model number on the bottom for the electricity meter.
Once you have the electricity meter model number you could look it up on our SMETS 1 or SMETS 2 Meter pages in order to work out if it is SMETS1 or SMETS2.
For further details on how to operate your meter see our manuals on our Documents page. (Updated: 2020-02-07)

Does my meter produce my bill?
Although your meter calculates your bill so that the cost can be shown on your IHD (In Home Display), your supplier will calculate and produce a bill independently of the meter readings collected from your meter. Suppliers do this so that they can produce a bill even if the communications to your meter is broken, i.e. requires an estimated bill. (Updated: 2020-02-09)

Who pays for the meter electricity?
The customer does not pay for the electricity used to power the meter directly as the meter takes its own power from a point before measurement takes place. The power used by the meter will fall into distribution losses which also includes the energy lost through the distribution cables as well. This was also the case with traditional meters.
Ultimately all customers pay for this as a percentage increase which is applied by area. For a technical explanation see Electricity Distribution System Losses. (Updated: 2020-08-19)

How often is data pulled from the meter?
Suppliers will try to contact your Smart Meter once a day to retrieve alarms and alerts. Meter readings will also be collected based on your agreement to have them recorded at monthly, daily or 30 minute intervals. (Updated: 2022-01-15)

What do the indicators mean on a SMETS2 Comms Hub?
The comms hub sits on top of the SMETS (Smart Meter Equipment Technical Specifications) electrcity meter and has a series of LED indicators showing the functional status of the metering system. Each LED has a legend shown below:
This shows the status of the hub's software. You should see a green light flashing every five seconds.
Shows your communication hub's ability to communicate with your supplier. If your meter is connected, you'll see a green light flashing every five seconds. This light may be off if your meter is using the MESH network to communicate.
This light may be on if your meter is connected and communicating through another network (this network has been built to allow more meters to communicate in areas with poor or no signal).
This light shows the connection status of your electricity meter, gas meter and/or IHD with your communications hub on the HAN (Home Area Network). If connected, you'll see a green light that flashes every five seconds.
This light tells you if a gas meter is connected; you should see a green light flashing every five seconds. If you don't have a gas meter installed, this light will be off.
(Updated: 2020-04-09)

Are SMETS2 meters compatible with storage heaters?
Yes. A fifth meter output is required to control the storage radiator load - 5 terminal meters are now available from most suppliers. (Updated: 2021-02-12)

What is a cut-out?
A cut-out is a piece of electrical equipment that forms the link between your DNO's (Distribution Network Operator) electricity cable and the internal wires in your property. It contains a large sealed fuse that can only be replaced by the DNO. Certain older cut-outs are inadequate and will need to be upgraded by the DNO as part of your Smart Meter installation. See this document for the various types of cut-out. (Updated: 2021-04-25)

If my electricity and gas is with different suppliers, what happens?
If your electricity and gas is with different suppliers, each supplier will contact you to make an appointment to install a smart meter for the fuel they supply to you. SMETS2 equipment has been designed to a particular standard so that all the meters and In Home Displays can talk together, this way you only need one In Home Display which will normally be supplied by the first supplier who installs a smart meter in your home. However, the earlier SMETS1 standard did not always interoperate unless the meters were on the same system, and even then support for interoperability by suppliers was poor. (Updated: 2019-10-21)

Will electric SMETS1 communicate with gas SMETS2, and vice versa?
Both meters need to the same SMETS standard. So if either your electricity or gas SMETS1 meter goes faulty they are likely to both be replaced with SMETS2 meters. (Updated: 2021-02-12)

What is Market-wide Half Hourly Settlement?
Market-wide Half Hourly Settlement (MHHS) will allow the electricity industry to move way from average consumption profiles for customers to using half hourly data.
Currently domestic and small business electricity use is modelled on a small number of average usage profiles. Obviously when you add up what was supplied and what was used they are not the same because of the use of average profiles. So the use of half hourly data will improve this and means that suppliers will have a more accurate wholesale energy bill.
This could improve customers' bills as the commercial risk for suppliers is slightly reduced.
This does not change tariffs for customers or what data domestic customers allow their smart meters to send unless they agree. (Updated: 2021-06-17)

How does a smart meter work?
A smart meter works by communicating with your energy supplier through a system operator, so the company will always have an accurate meter reading and there's no need for you to take a meter reading yourself. A communications module on the electricity meter talks to the gas meter and IHD (In Home Display). Smart meters can work in a variety of different ways, including using wireless mobile phone type technology to send data. See our How They Work page for more information. (Updated: 2019-10-21)

Can my supply be turned off remotely?
Smart meters have the facility to remotely disconnect and reconnect both the electricity and gas supply. However, most suppliers seem to have decided it is too dangerous to remotely disconnect or reconnect, as in the case of disconnection they cannot always be sure that the customer isn't relying on a supply for serious health reasons and in the case of reconnection the customer may have left a cooker on for example. (Updated: 2015-01-23)

How do I top-up my smart meter PAYG if the mobile network is down?
Normally your PAYG (Pay As You Go) top-up will be sent automatically to the smart meter, however, if the communications link through the mobile network is not available then this cannot happen.
Firstly you can use the emergency credit that most suppliers offer. If that runs out you can enter the long authorisation number that you received when you paid for the credit into the meter or IHD (In Home Display) to apply your credit. This very difficult to do on the meter so use the IHD if you can. (Updated: 2019-10-21)

Is my energy use "IMP KWH", "EXP KWH, or "IMP KVARH"?
The IMP KWH should be used to show how much electricity you have used.
The EXP KWH is for how many kWhs you've pumped out to the National Grid, which is only relevant if you've got something generating electricity such as solar panels.
IMP KVARH is only used by distribution companies as it helps understand the current flowing in the supply cables. (Updated: 2021-04-09)

Are Smart Meters safe from hackers?
All smart meters in Britain have to conform to the same strict security standards, and go through testing against the Commercial Product Assurance (CPA) Security Characteristics by an approved laboratory.
The security system consists of many layers and has been design by Government Communications Headquarters (GCHQ). The National Cyber Security Centre (NCSC) is involved in ongoing reviews.
Smart meters use their own bespoke wireless connection to communicate with suppliers. This wireless connection has been built to be extremely secure, and is encrypted to prevent hackers being able to attack electricity supplies.
There are also monitoring systems in the background known as "Anomaly Detection" which look for unusual patterns of data across the communications network.
So they're not connected to the internet and only hold information on your energy consumption. Not only are smart meters hard to hack, there would be no point doing it anyway. (Updated: 2021-04-23)

How do Smart Meters send data?
The communications hub or comms hub sitting immediately onto top of your electricity meter is responsible for receiving and sending all data. This data can be meter readings, commands or alerts.
The comms hub uses the Home Area Network (HAN) to talk to the electricity, gas and IHD (In Home Display) devices. To save battery power the gas meter communicates only every half-hour and so the comms hub stores a copy of the gas meter data for querying when required. This copy is known as the gas mirror or Gas Proxy (GPF).
The comms hub uses the Wide Area Network (WAN) to talk to the company responsible for collecting the data and passing it on to other businesses such as suppliers; for the latest SMETS2 meters this company will be the DCC (Data Communications Company) which the government has set up especially for this role.
Depending on the Communications Service Provider, which varies by areas of the UK, the radio technology can change depending on what works best in a local area. Sometimes your comms hub will communicate directly with DCC and sometimes it will talk through other comms hubs around you to reach a particular comms hub which has direct communications with DCC. This form of communications looks like a mesh when you draw out the possible links between meters and is therefore known as a Mesh network. (Updated: 2020-11-07)

What is the HAN range?
The range of the Smart Meter HAN (Home Area Network) is about 15m, but this is reduced by obstructions such as walls and doors. Where the meter is a long way from the location of the IHD (In Home Display), or thick walls are in the way, the current technology (Zigbee at 2.4GHz) won't work. This could be the case for up to 30% of properties.
A different communications method (Zigbee 868MHz) available from mid 2020 will improve this for about 3.5% of properties but that still leaves a large number for whom Smart Meters won't work.
For these final properties, for example where meters are in a basement a long way from the customer's IHD, a separate company has been set up to investigate solutions, prepare contracts and procure the equipment. The company is the Alt HAN Co Ltd and solutions are expected in 2021. (Updated: 2021-10-03)

Can a Smart Meter replace my Radio Teleswitch?
Yes a Smart Meter can provide similar functionality to the Radio Teleswitch System (RTS). RTS is used to stagger the switch on and off times of tariffs such as Economy 7 so that a surge in power doesn't occur from all the storage radiators in the country switching on at the same time.
If you are on a tariff switched by RTS we recommend you speak to your supplier to get a Smart Meter and ask what tariff you can move to. The RTS service uses the BBC Radio 4 long wave signal and is planned to end in March 2023. (Updated: 2021-04-25)

Why are Smart Meters more accurate?
It is a bit misleading to say Smart Meters are inherently more accurate than traditional meters as they all must meet the same standards. The improved accuracy is around billing, as meter readings will be collected automatically and stamped with the precise date/time. (Updated: 2017-08-14)

Why is two way communications important?
Smart meters send meter reading and event information to suppliers. Supplier can send product and payment details to the meter when you want to change your product or payment terms. Additionally this two way communications supports Pay As You Go for energy. (Updated: 2018-05-05)

Are there special considerations for the location of a Smart Meter?
When a meter fitter first arrives at your premises they will usually check the signal available with a special tool and decide if the installation can go ahead; in some cases an additional aerial or alternate communications system can be used if the signal is poor. The Smart Meters must be fitted in place of or near your old meters as it is too expensive to move the incoming power cable and gas connection, and not good to have long cables from the main fuse (cutout) to the meter. (Updated: 2018-07-01)

Which supplier do I contact regarding my meter?
Always contact your current supplier regarding any problems with your meter. The installing supplier no longer has any responsibility for it. (Updated: 2021-08-07)

Why are there different WAN communication protocols North and South?
DCC went out to tender to find CSPs (Communication Service Providers) to provide the WAN (Wide Area Network) for three regions: North, Central and South. The winners of this commercial process offered different technologies reflecting the different population density and terrain in the regions :
Arqiva Limited for CSP North region with a 15-year contract worth £625M using Long-Range Radio communications.
Telefónica (O2) for the CSP Centre (Midlands, East Anglia and Wales) and South (south of England) regions using the 2G/3G cellular radio communications network. The two Telefonica contracts over 15 years are worth £1500M.
The contracts were awarded in 2013. (Updated: 2021-11-15)

What is a smart meter?
A Smart Meter is a new kind of meter to measure your energy, they are available for electricity and gas. Smart meters allow communications to and from your energy supplier and distribution network operator, and they can therefore can send meter readings automatically. An In Home Display will be provided with your meter to allow you to see how much energy you are using and what it is costing. There have been a number of standards in the UK, but the latest is called a SMETS2 meter. (Updated: 2018-07-01)

Can I have a smart meter if I'm a prepayment customer?
Yes. Smart meters work in both credit and prepayment modes. In fact, prepayment customers will have more flexible payment options available to them with smart meters, including remote top-up facilities. (Updated: 2014-12-20)

How do I read a smart meter?
It is possible to read information from your smart meter, unfortunately there are many different makes out there with different controls, so please check our Documents page or contact your supplier for additional information. (Updated: 2019-10-21)

Are Three-phase SMETS2 meters available yet?
The SMETS2 standard covers Three-phase meters but few suppliers have put in orders for them yet. They are likely to appear over the next couple of years.
See Wikipedia for an explanation of Three-phase power. (Updated: 2021-02-12)

What is a 5 terminal meter?
In addition to the usual live and neutral in, and live and neutral out, a 5 terminal meter has another live output. This additional output is switched according to your tariff and is usually connected to off peak heating to take advantage of times when the electricity is cheaper. (Updated: 2021-04-09)

What is a traditional meter?
A traditional, dumb or legacy meter are all names for the kinds of mechanical or electronic meters that have been used for the last 100 years. These older meters do not have two way communications. The preferred term for them is a traditional meter. (Updated: 2015-05-29)

How do I read an In Home Display?
The In Home Display (previously known as Smart Meter Display or Home Energy Monitor) has been designed to provide information to customers in their homes, and so should be easy to understand. For both electricity and gas it will display your energy consumption in either pounds and pence or kilowatt hours, helping you understand how you are using energy in your home at any given point in time. Unfortunately there are many different makes out there with different controls, so please check our Documents page or contact your supplier for additional information. (Updated: 2019-10-21)

Are the meters battery powered?
The electricity meter is mains powered but the gas meter is battery powered. The gas meter battery can be replaced by a Smart Meter Installer and is excepted to last the life of the meter (10 to 15 years), however, its life can be greatly reduced heavy communications such as repeated firmware updates. (Updated: 2016-01-27)

Could my IHD link to my neighbour's meters?
Your IHD (In Home Display) is paired to your own meters by the installer. It won't pick up information from your neighbours and can't be used in another house. If you need a replacement IHD this will have to be paired with your meters. (Updated: 2016-10-04)

Do I require a broadband connection or wi-fi in my home to be able to use a smart meter?
Smart meters don't need a broadband connection or wi-fi in your home as they use either the GSM (Global System for Mobile communications) mobile networks just like your mobile phone, or use a local mesh communications network (DCC only) to hop from meter to meter until a link to the GSM mobile network is found. (Updated: 2018-07-01)

Do smart meters work with home generated renewable energy?
Traditional meters are only capable of recording consumption and consequently don't take into account any energy generated by a household. If you have or are planning to install solar panels or any other renewable energy generating system in your home, a smart meter will enable you to measure how much energy you produce. The smart meter will also calculate whether or not there is a surplus which you could sell back to the grid.
However, as this is not a common requirement suppliers have been slow in implementing systems to support it - you will have to shop around for the supplier which can support your requirements. (Updated: 2019-10-21)

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