Your electricity bill shows the household’s total consumption, but it often does not reveal which appliances are responsible. Does the old refrigerator really use more energy than the new television? How much power do the router, games console and home-office equipment consume in standby? And would using the tumble dryer less often make a meaningful difference?
A smart plug with energy monitoring can help answer questions like these. It sits between the wall socket and an appliance and records the power drawn by the connected device. Depending on the model, the current wattage and accumulated kilowatt-hours are shown on a display, in an app or in a smart-home system.
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Measuring the electricity use of individual appliances
The basic process is simple: insert the measuring plug into the wall socket, connect the appliance and start recording. Do not look only at the instantaneous power in watts. That value merely shows how much power the appliance needs at that moment. Electricity costs, by contrast, depend on the energy consumed over time, measured in kilowatt-hours.
A 100-watt device running for one hour consumes 0.1 kilowatt-hours. For a rough cost calculation, multiply that consumption by your personal electricity price per kilowatt-hour. A television may draw a moderate amount of power while operating, yet still matter because it is used for many hours each day. A high-power appliance such as a kettle, on the other hand, normally runs for only a few minutes.
For a meaningful result, the measuring period should match the type of appliance:
- Constant loads: A short reading may be enough for a lamp or a simple power supply.
- Routers, NAS devices and aquarium equipment: Several days or a full week provides a better picture of continuous operation.
- Refrigerators and freezers: Measure for at least several days because the compressor operates in cycles.
- Washing machines, dishwashers and tumble dryers: Compare several typical programmes.
The German non-profit advice service co2online provides a practical German-language guide to calculating consumption and choosing a suitable measurement period.
Which household appliances actually use a lot of electricity?
The appliance with the highest wattage is not automatically the largest energy consumer. Power, running time and frequency of use all matter. Germany’s Federal Environment Agency identifies refrigeration, dishwashing, laundry, process heat, cooking, process cooling and information and communication technology among the relevant areas of household electricity use.
These appliances are particularly worth measuring:
- Tumble dryers: They are often among the more energy-intensive individual appliances because they generate heat and can run for a long time.
- Old refrigerators and freezers: They operate around the clock. Even a seemingly modest continuous load can add up over a year.
- Washing machines and dishwashers: Heating phases often account for much of their consumption, although a single programme may not be representative.
- Entertainment electronics: Televisions, games consoles, AV receivers and streaming devices can matter because of long operating times or standby consumption.
- Computer workstations: If you want to assess the complete workstation, measure the desktop PC, monitor, speakers, printer and accessories together where appropriate.
- Routers, NAS devices and network equipment: Their power draw is usually modest, but continuous operation makes the annual total interesting.
- Aquarium and terrarium equipment: Lighting, pumps and heaters may operate continuously or on a schedule.
According to the German Federal Environment Agency, private households in Germany consumed around 133 billion kilowatt-hours of electricity in 2024. Despite more efficient appliances, consumption had fallen only to a limited extent compared with 2008, partly because households owned more and larger devices. This makes it useful to look not only at an energy-efficiency label but also at actual consumption in your own home.
Energy meter, smart plug or sub-meter?
Not every plug with a display is automatically smart. A clear distinction helps when choosing.
Basic plug-in energy meter without Wi-Fi
A basic plug-in energy meter normally has an integrated display and is operated directly on the device. It needs no user account, app or internet connection, which can be an advantage for privacy. It is also well suited to a single, time-limited measurement.
Possible disadvantages include limited data storage and less convenient analysis. If you want to compare several appliances over a number of weeks, you may have to record the readings manually.
Smart plug with energy monitoring
A smart plug combines measurement with an app, schedules and, in some cases, voice control. Daily, weekly and monthly values are often easy to review. Depending on the platform, cost estimates, notifications and automations may also be available.
This convenience requires additional technology. Depending on the model, you may need Wi-Fi, a Zigbee or Thread hub, a Matter-compatible system or a cloud account.
Sub-meter for a circuit
A sub-meter is not simply plugged into a socket. It measures a larger section of the installation or a dedicated electrical circuit. This can be useful when several appliances share a supply, for example in a workshop, server area or separate apartment.
Fixed appliances and work inside an electrical distribution board require installation by a qualified electrician. A smart plug is not a substitute for a sub-meter or professional electrical work.
What determines measurement accuracy?
A claim such as “high precision” says little by itself. The measuring range, resolution, measurement method and conditions under which the manufacturer states the accuracy are what matter. For most household comparisons, a good indicative measurement is sufficient. At very low loads, however, the difference between two meters can be larger than expected.
This matters especially for standby consumption. Some meters do not measure very low power reliably or show a stable value only above a certain load. When investigating routers, chargers or entertainment equipment that appears to be off, check the following specifications:
- the lower end of the measuring range and the resolution,
- stated accuracy at low loads,
- measurement of changing or very short loads,
- storage of kilowatt-hour values over longer periods,
- the plug’s own power consumption.
For a fair comparison, measure different appliances with the same electricity price, over similar periods and under conditions that are as comparable as possible. A brief snapshot is not sufficient for a refrigerator or an appliance with heating phases.
App, Wi-Fi, Zigbee, Thread or Matter?
The wireless technology affects usability, resilience and expandability. A Wi-Fi plug often connects directly to the existing router without an additional hub. In return, it may depend more heavily on the manufacturer’s app and cloud service.
Zigbee and Thread plugs usually need a central bridge or compatible hub. They can be easier to integrate into a larger smart-home system. Matter is intended to simplify interoperability between platforms, but the label alone says nothing about measurement accuracy, local data storage or app quality.
Before buying, check:
- Are watts and kilowatt-hours shown separately?
- Are daily, weekly and monthly reports available?
- Can data be exported or stored locally?
- Does energy monitoring work without an internet connection?
- Is a hub required?
- Does the model support Apple Home, Google Home, Alexa, Matter or Home Assistant?
Privacy and smart plugs
A smart plug does not record conversations, but consumption data can reveal household routines. Regular load patterns may indicate when somebody is at home, when they work or how often particular appliances are used.
It is worth reading the privacy policy before setup. Pay particular attention to these questions:
- Is a user account mandatory?
- Where are measurement and usage data stored?
- Which app permissions are requested?
- Is data encrypted in transit?
- How long does the supplier provide security updates?
- Can data be deleted or exported?
- Is local control available without mandatory cloud access?
The German consumer advice organisation Verbraucherzentrale recommends checking these points before buying a smart-home product. If you want to disclose as little data as possible, consider a meter with its own display or a system that analyses data locally.
Automations are useful, but not for every appliance
A smart plug can do more than measure. Schedules, consumption thresholds and push notifications can help monitor routines. For example, it may send an alert when an appliance runs for unusually long or switch off entertainment electronics at a particular time.
Any automation must be appropriate for the connected appliance. Problems can arise if a device starts automatically after power is restored or requires a manual operating sequence. Before use, also establish how the plug behaves after a power cut: does it remain off, switch on or restore its previous state?
For heaters, high-power appliances, extension strips and devices with high continuous loads, rated current, maximum switching capacity, heat generation and the manufacturer’s approval are especially important. Connect a refrigerator, freezer, washing machine or dryer only if the plug is expressly suitable for that type of load. Automated cut-off is generally a poor choice for safety-critical appliances.
Smart meter or smart plug?
The terms are often confused. A smart plug normally measures only the connected appliance. In Germany, an “intelligent metering system” as defined by metering legislation consists of a modern meter and a smart-meter gateway. It records consumption at the metering point for the household or installation and enables secure communication.
A smart meter therefore does not replace measurement at an individual appliance. Conversely, a plug cannot measure the total consumption of a home. A plug-in meter is suitable when you want to know how much one appliance uses. For an overall analysis or a fixed circuit, a sub-meter or professionally installed measurement system is more appropriate.
Buying checklist
The right solution depends on your objective. For occasional measurement without a cloud service, a basic plug with a display is often sufficient. For long-term analysis and automation, compatibility with your smart-home ecosystem matters.
- Measurement only: A display, no account and no Wi-Fi may be enough.
- Long-term data: Look for kilowatt-hour storage, history and export functions.
- Standby analysis: Check low-load resolution and documented accuracy.
- Automation: Compare schedules, thresholds and behaviour after a power cut.
- Privacy first: Prefer local storage and local control.
- Smart-home expansion: Check compatibility with Wi-Fi, Zigbee, Thread, Matter or Home Assistant.
- High loads: Verify rated current, continuous-load capability and thermal safety for the specific model.
Conclusion: measure first, then save where it matters
A smart plug with energy monitoring makes the energy use of individual appliances visible and turns assumptions into comparable figures. It is particularly useful for always-on devices, old large appliances, home-office workstations and entertainment electronics with standby consumption.
Apps and voice control are not the only relevant features. Measuring range, resolution, long-term recording, privacy, local functions and electrical load capacity are at least as important. Measurements over several days or across several typical programmes give a much more realistic picture than a quick glance at the current wattage. This helps identify the appliances that genuinely use the most electricity and target savings where they can make the greatest difference in your household.
Frequently asked questions about smart plugs with energy monitoring
What is the difference between a plug-in energy meter and a smart plug with energy monitoring?
A basic energy meter normally shows values directly on an integrated display. A smart plug can additionally report consumption through an app or smart-home system and switch the connected appliance. Accuracy, data storage and cloud dependence vary between models.
How long should an appliance be measured?
A short reading may be enough for a constant load. Refrigerators, freezers, routers and NAS devices should be measured for several days or a week. For washing machines, dishwashers and tumble dryers, several typical programmes are more representative than a single cycle.
Can a smart plug measure standby consumption reliably?
That depends on its measuring range and resolution. At very low power levels, a meter may be inaccurate or unstable. Check the manufacturer’s specifications for low loads and use longer measurement periods where possible.
Can a smart plug calculate electricity costs automatically?
Many apps let you enter your electricity price and convert measured kilowatt-hours into estimated costs. The result is only as current as the tariff you enter and may not automatically include every component of an electricity bill.
Is a smart plug the same as a smart meter?
No. A smart plug normally measures only the connected appliance. A smart metering system records consumption at the household’s metering point and, in Germany, consists of a modern meter and a smart-meter gateway.