A smart plug is the cheapest way to automate something and the easiest way to find out what a device really uses. It is also the product category where it is easiest to buy the wrong thing: a plug that only works through an app and a remote server, a relay too weak for a heater, or a metering chip that reports once a minute when you wanted live data. This guide goes through the questions worth asking before you buy, using a few current plugs as examples of each approach.

Question 1: which radio, and who controls it?

The radio decides how the plug joins your home and what happens when the internet goes down.

Wi-Fi plugs connect straight to your router. No hub is needed, which makes them the simplest to start with. The catch is that many Wi-Fi plugs talk only to the manufacturer's cloud. For local control you want a plug with a documented local interface: an HTTP API, MQTT or Matter. Each Wi-Fi plug is also another client on your 2.4 GHz network, which matters once you have dozens.

Zigbee plugs need a coordinator (a USB adapter with Zigbee2MQTT or ZHA, or a vendor hub), but they are local by design and every mains-powered Zigbee plug also acts as a router that strengthens the mesh for battery sensors. If you already run Zigbee, plugs are a cheap way to improve coverage.

Matter plugs come in two flavours. Matter over Wi-Fi behaves like any Wi-Fi plug on the network side. Matter over Thread needs a Thread border router and, like Zigbee, the plug strengthens the Thread mesh. Either way, Matter control is local by specification, and one plug can be shared between Apple Home, Google Home, Alexa and Home Assistant.

Question 2: what exactly does "local" mean for this plug?

Look for one of these, and confirm it in the manufacturer's documentation rather than on the box:

  • A documented local API. Shelly is the best known example. The Plug S Gen3 has a built-in web interface, MQTT, webhooks and an RPC API you can call directly, for example http://<ip>/rpc/Switch.Set?id=0&on=true to switch it on and Switch.GetStatus to read power, voltage and current.
  • Open firmware. Some plugs ship with Tasmota already installed. The Nous A1T is one: an ESP-based Wi-Fi plug sold with Tasmota, MQTT and power metering out of the box, with no cloud account required. Others can be flashed with Tasmota or ESPHome, but only if they use an Espressif chip, and many newer models do not.
  • A local standard. Zigbee and Matter plugs are controlled locally whatever brand they are.

A useful test is to block the plug's internet access in your router for a day. If schedules, automations and metering still work, it is genuinely local.

Question 3: is the relay strong enough?

This is where people get caught. The rated maximum is printed on the plug and in the datasheet, and it differs a lot between models:

Plug Radio Rated maximum
IKEA INSPELNING (EU) Zigbee 16 A, 3680 W resistive; 300 W motor load
Nous A1T Wi-Fi (Tasmota) 16 A, 3680 W
Shelly Plug S Gen3 Wi-Fi + Bluetooth, Matter 12 A, 2500 W (resistive load only)
Eve Energy (Matter) Thread 11 A, 2500 W; incandescent lamps up to 240 W

Three practical rules follow:

  1. Leave headroom. A 2000 W fan heater running for hours on a 2500 W plug is within the rating, but the plug will run warm. For heaters, kettles, washing machines and anything above about 2 kW, pick a 16 A model or do not use a plug at all.
  2. Read the fine print on load types. Motors, compressors and some LED drivers draw a large inrush current. IKEA lists only 300 W for motor loads on a plug that is otherwise rated at 3680 W.
  3. Do not chain plugs or use them with extension leads carrying high loads. The weakest contact sets the limit.

Question 4: will it fit your socket?

In Poland, wall sockets are type E, with a grounding pin. Many plugs sold across Europe are built for type F (Schuko) and have a "hybrid" CEE 7/7 plug that fits both. Check the datasheet. Shelly, for example, specifies a CEE 7/7 plug for the Plug S Gen3, which fits type E sockets, and Eve lists type E and F sockets for the European Eve Energy. The outlet on the front of the plug is usually type F, which accepts the hybrid plugs on almost all appliances sold in Poland. Also check the plug's width if you want two side by side in a double socket.

Question 5: how good is the energy metering?

Not every smart plug measures energy, and the ones that do vary in what they report and how often:

  • What is measured. Good plugs report active power (W), voltage, current and cumulative energy (kWh). INSPELNING reports all four over Zigbee. The Shelly Plug S Gen3 lists a voltmeter, ammeter and power and energy meters.
  • How often you get updates. Tasmota sends a full telemetry report every TelePeriod seconds (300 by default; you can lower it) and also reports changes as they happen. Zigbee plugs report on change, subject to reporting thresholds set in the coordinator. If you want to see a washing machine's cycle in detail, shorter reporting intervals matter.
  • Where the total lives. If the plug keeps a running kWh total, a restart or power cut should not reset it. If your automation platform calculates energy from power readings, gaps in reporting become gaps in the total. For a home energy dashboard, prefer a plug that reports a cumulative kWh value.
  • Accuracy. Manufacturers rarely publish accuracy for consumer plugs. Treat the readings as good for comparisons and spotting standby waste, not as a billing-grade meter. If you need precision, compare against a known resistive load such as a kettle with a rated power, or against your electricity meter over a day.

Question 6: what happens after a power cut?

Check what the plug does when power returns: stay off, turn on, or restore its previous state. For a fridge or a freezer you want "on" or "restore". For a heater you may want "off". Shelly, Tasmota (PowerOnState) and most Zigbee plugs let you choose. If the plug can only restore the last state, think about what that means for each device on it.

A quick decision guide

  • You already run Zigbee: a Zigbee plug with metering, such as INSPELNING, is cheap, local and strengthens the mesh.
  • You want Wi-Fi, local control and no tinkering: a plug with a documented local API or pre-installed Tasmota, such as the Shelly Plug S Gen3 or Nous A1T.
  • You use Apple Home or several ecosystems: a Matter plug. Choose Matter over Thread if you have border routers, Matter over Wi-Fi if not. On the Shelly Plug S Gen3, note that scripting is not available while Matter is enabled.
  • High loads (heaters, washing machines): a 16 A model with headroom, or a properly installed relay in the circuit instead of a plug.

Common mistakes

  • Buying a cloud-only plug because the box says "works with Home Assistant". That usually means a cloud integration.
  • Plugging a 2 kW heater into a 10 A or 12 A plug and leaving it running unattended.
  • Assuming every plug measures energy. IKEA's TRETAKT, for example, only switches; INSPELNING is the one that meters.
  • Forgetting firmware updates. Local plugs still need them; schedule a check every few months.