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Energy Meters

Whole-house consumption in real time — and the first honest step towards a smaller bill.

Pen-and-ink drawing of a P1 energy meter dongle with its cable

A smart plug tells you what one appliance costs. An energy meter tells you what the house costs, second by second, including the things you cannot plug in: the boiler, the oven, the shower, the heat pump, the lighting circuits. It is the single most informative device you can add, because almost nobody guesses their own consumption correctly.

How you connect one depends on where you live and what your utility meter offers. In the Netherlands and Belgium, virtually every modern meter has a P1 port — a standardised serial socket that streams live readings for electricity and often gas and water too. Plug a dongle in and you are done in two minutes, with no electrical work at all. Norway and parts of Scandinavia have the equivalent HAN port. Germany typically has neither, so readers there clip over the meter’s blinking infrared LED and count pulses optically.

Where no port exists, the alternative is CT clamps — current transformers, jaws that clip around a live cable and measure the magnetic field it produces without cutting into it. These go in the consumer unit, they can measure individual circuits rather than just the total, and they are electrician territory.

What to look for

What your utility meter actually offers

Look at it before buying. A P1 socket (Netherlands, Belgium) or HAN port (Norway) means the cheapest and easiest option. A blinking LED and no port means an optical reader. Neither means CT clamps in the consumer unit.

Whether it measures both directions

If you have or plan solar panels, you need a bi-directional meter that separates what you import from the grid from what you export back. A meter that only reports a single total is close to useless once you generate your own power.

Single-phase or three-phase

Most homes have one live conductor (single-phase). Many Dutch, German and Belgian homes have three, which allows higher total load. A single-phase meter on a three-phase supply will only ever see a third of your consumption, which is a common and expensive mistake.

Whether it needs an electrician

P1, HAN and optical readers are genuinely plug-in. CT clamps and DIN-rail meters go inside the consumer unit alongside live busbars and are not a DIY job in most jurisdictions.

Local or cloud

Some meters report straight onto your network. Others send readings to the manufacturer’s servers and hand them back to you, which means an internet outage takes your energy data with it. For something you want to automate against, local is markedly better.

Accuracy, and whether it needs to be billable

For behaviour change, 1–2% accuracy is ample. If a reading has to be legally billable — sub-metering a tenant or a shared charge point — it must be MID-approved, which is a certification, not a spec sheet claim.

The shortlist compared

BrandModelConnectionTypeDirectionLocalIndicative price
HomeWizardWi-Fi P1 MeterWi-FiP1 portBi-directionalYes€30
HomeyEnergy DongleWi-FiP1 portBi-directionalYes€39
energieleserstromleser.oneWi-FiOptical (LED pulse)Bi-directionalYes€75
frientElectricity Meter Interface 2ZigbeeOptical, P1 or HANBi-directionalYes€80
AeotecHome Energy Meter 8Z-Wave3 × 60 A CT clampsBi-directionalYes€80
IOmeterSmart Meter868 MHz + Wi-Fi bridgeOpticalBi-directionalYes€80
TibberPulseWi-FiP1, HAN, KM or CTBi-directionalPartly€90
PowerfoxPoweroptiWi-FiOpticalBi-directionalCloud only€90
EmporiaVue Energy MonitorWi-FiCT clamps, per-circuitBi-directionalYes€100
ShellyPro 3EMWi-Fi, BLE, LAN3-phase CT, 120 or 400 A4-quadrantYes€120
PlugwiseSmile P1Wi-Fi or EthernetP1 portBi-directionalYes€120
HomeWizard3-Phase kWh MeterWi-FiWired, DIN rail, MIDBi-directionalYes€130

Prices move constantly and vary by country, so we give an indicative band rather than a figure that would be stale within a month. Check the brand's own store for the current price.

The picks in detail

HomeWizard Wi-Fi P1 Meter

Wi-Fi, P1 port

If you have a P1 socket, start here. Around €30, installed in the time it takes to open the meter cupboard, and on a DSMR 5.0 meter it draws its own power from the port so there is no adapter to find a socket for. DSMR (Dutch Smart Meter Requirements) is the specification Dutch and Belgian meters are built to; version 5.0 and later can power a dongle directly.

It reads gas as well as electricity, which most CT-based systems cannot do at all. The cable is short, so if your router is far from the meter cupboard, check Wi-Fi coverage there first.

  • Cheapest route to whole-house monitoring
  • Powered by the meter itself on DSMR 5.0
  • Reads electricity and gas
  • Tiny at 45 × 45 × 15 mm
  • Very short cable
  • Needs a P1 port, so Netherlands and Belgium mainly

Homey Energy Dongle

Wi-Fi, P1 port

The splitter is the detail worth paying for. A P1 port is a single socket, and increasingly two devices want it — your monitoring dongle and, say, an EV charger that needs live consumption data to do load balancing. This one passes the port through rather than occupying it, which avoids an awkward choice later.

Older meters that cannot power the port are handled with the supplied USB cable. Reads gas and water where those are linked to the electricity meter.

  • Plug and play on any P1 port
  • Also reports linked gas and water meters
  • Built-in splitter frees a second P1 slot
  • Wi-Fi 6 and Bluetooth 5 LE
  • P1 markets only

Shelly Pro 3EM

Wi-Fi, Bluetooth and LAN

The serious option for a three-phase house, and DIN-rail mounted so it lives neatly in the consumer unit. DIN rail is the standard metal mounting strip inside a breaker box that components clip onto.

It does 4-quadrant measurement, meaning it tracks import and export of both real power (the part that does work) and reactive power (current that sloshes back and forth without doing work, caused by motors and transformers). That is more detail than most homes need, but it is the level at which you can actually diagnose a strange bill.

  • Proper three-phase measurement
  • Ethernet and Wi-Fi usable simultaneously
  • Reports voltage, power factor and reactive power
  • Clamps available in 120 A and 400 A
  • Consumer-unit installation, so an electrician
  • Can show odd negative readings with certain loads

Aeotec Home Energy Meter 8

Z-Wave

The Z-Wave choice, and a good one if your network is already Z-Wave and you would rather not add another Wi-Fi client. Three non-invasive clamps mean you can either monitor three phases or split a single-phase supply across three circuits of interest. Bi-directional, so solar export is reported separately rather than confusingly netted off.

  • Three 60 A clamps, so three-phase or three circuits
  • Z-Wave 800 series with S2 security
  • Separates grid import from solar export
  • IP44 rated
  • Some users report awkward pairing in secure mode

Emporia Vue Energy Monitor

Wi-Fi

The one to choose if you want to know which circuits are responsible rather than just the total. With clamps on individual circuits you can see the difference between the kitchen and the heat pump, which is where actionable insight actually lives. One-second data resolution makes appliance-level patterns visible. It is the most invasive install here.

  • Per-circuit monitoring, not just the whole house
  • One-second resolution
  • Identifies solar overproduction and wasteful appliances
  • Involved installation, professional recommended

Plugwise Smile P1

Wi-Fi or Ethernet

The compatibility pick: it handles old DSMR V2 meters as well as current V5 ones, which matters if your meter predates 2015. The Ethernet port is the real reason to choose it — meter cupboards are frequently the worst Wi-Fi spot in a house, and a cable removes the problem entirely. Which is just as well, because the Wi-Fi radio is the unit’s weak point.

  • Works with every Dutch and Belgian meter from DSMR V2 to V5
  • Ethernet option for a rock-solid link
  • No subscription
  • Bi-directional
  • Built-in Wi-Fi antenna is weak, so Ethernet is often necessary

IOmeter

868 MHz radio plus Wi-Fi bridge

A clever answer to the commonest practical problem: no Wi-Fi in the cellar. The optical head sits on the meter and talks to a bridge elsewhere in the house over 868 MHz sub-gigahertz radio, which passes through concrete far better than 2.4 GHz — up to 50 m or three floors. The bridge stores readings if your connection drops, so the history has no holes.

  • No Wi-Fi needed at the meter itself
  • Bridge buffers readings during an internet outage
  • Core runs about 18 months on two AA cells or USB-C
  • Sold for the German market
  • Not supported on meters over eight years old

frient Electricity Meter Interface 2

Zigbee

The flexible option: one product family covering optical pulse reading, P1 for the Benelux and HAN for Norway. Battery powered and Zigbee, so it needs no socket and no Wi-Fi at the meter. The failure mode to know about is optical mode on a meter whose LED pulse is dim or oddly timed, where readings can drift.

  • Battery powered, around two years on two AA cells
  • Variants for optical, P1 and HAN
  • Small enough to fit inside a fuse box
  • Zigbee, so no extra Wi-Fi client
  • Can misread meters with an unclear LED pulse

Powerfox Poweropti

Wi-Fi, cloud

Easy to fit and well made, but be clear about the architecture: readings travel to Powerfox’s servers and come back to you from there. An internet outage or a service problem takes your energy data with it. For a device whose whole job is feeding automations and dashboards, that is a meaningful weakness compared with the local alternatives above.

  • Genuinely plug-and-play optical reader
  • Neat design with the sensor in the connector
  • Bi-directional
  • Requires the Powerfox cloud, so it stops working without internet

Tibber Pulse

Wi-Fi

Good hardware with a commercial string attached. The reader itself works broadly, but the features people buy it for — cost conversion, hourly tariff awareness, peak-usage tracking — require a Tibber electricity contract. If you are a Tibber customer it is an obvious choice; if not, the money is better spent elsewhere.

  • Market-specific P1, HAN, KM and CT versions
  • Supports load balancing for EV chargers
  • Reports per-phase or total load
  • Cost, tariff and peak features need an active Tibber contract

What you can actually do with the data

Monitoring on its own changes very little. Three things make it pay.

Find the standing load. Look at consumption at 3am, when nothing should be running. Most houses discover 150–400 W of permanent draw they cannot account for. Chasing that down with a rotating metering plug is the cheapest saving available.

Shift load to cheap hours. If you are on a dynamic tariff, live consumption plus hourly prices lets you run the dishwasher, charge the car and heat water when electricity is cheapest — occasionally at a negative price, when you are effectively paid to consume.

Feed load balancing. An EV charger that can see live household consumption will throttle itself rather than tripping your main fuse when the oven and the shower come on mid-charge. This is the most valuable single use of a P1 meter, and the reason the port pass-through on some dongles matters.

Anything inside the consumer unit is an electrician’s job. CT clamps and DIN-rail meters are fitted alongside live busbars carrying enough current to be lethal, and in most jurisdictions the work is legally restricted. P1, HAN and optical readers involve no electrical work at all, which is a good reason to prefer them where your meter allows.

Further reading

Frequently asked questions

What is a P1 port?

P1 is a standardised serial socket found on Dutch and Belgian smart meters that streams live readings for electricity, and usually gas and water too. A dongle plugs straight in with no electrical work, which makes it by far the easiest and cheapest way to monitor a whole house. Norway and parts of Scandinavia use an equivalent called the HAN port.

What is a CT clamp and do I need an electrician?

A CT clamp (current transformer) is a hinged jaw that clips around a live cable and measures the magnetic field it produces, so it reads current without the cable being cut. Because it is fitted inside the consumer unit next to live busbars, installation is an electrician’s job in most countries.

Do I need a bi-directional meter?

If you have solar panels, or might add them, yes. A bi-directional meter reports what you draw from the grid and what you send back separately, rather than giving one net figure. Without that distinction you cannot see self-consumption, and automations that respond to solar surplus have nothing to work with.

What is the difference between kW and kWh?

A kilowatt (kW) is a rate — how fast you are using electricity at this instant, like the speed on a speedometer. A kilowatt-hour (kWh) is a quantity — how much you used over time, like distance travelled. Your bill is in kWh; a live monitor shows kW.

Does the meter need to be MID-approved?

Only if the readings must be legally billable, such as sub-metering a tenant or charging someone for EV charging. MID refers to the EU Measuring Instruments Directive, and approval is a formal certification rather than a claimed accuracy. For understanding your own consumption, any meter accurate to 1–2% is entirely adequate.

Terms explained

P1 port
A standardised serial socket on Dutch and Belgian smart meters that provides live consumption data for electricity, and often gas and water. Devices plug directly in with no electrical work, and on DSMR 5.0 meters the port can also power the device.
CT clamp (current transformer)
A hinged sensor clipped around a live cable that measures the current flowing through it via the magnetic field it produces, without any need to cut or disconnect the wire.
DSMR (Dutch Smart Meter Requirements)
The specification Dutch and Belgian smart meters are built to. The version number matters in practice: DSMR 5.0 and later can supply power to a device plugged into the P1 port, while older meters cannot.
Bi-directional measurement
Recording energy flowing in both directions separately — imported from the grid and exported back from solar generation — instead of reporting a single net figure.
MID (Measuring Instruments Directive)
EU legislation setting the certification a meter needs before its readings may be used as the basis for billing someone. It is a legal approval, not simply a statement of accuracy.

More terms in the smart home glossary. Related questions: Why measure energy use at all? What is a P1 port? What is a CT clamp?