Home Energy Monitoring Systems: How They Work
A home energy monitoring system measures the current flowing through your electrical panel and turns it into watts, kilowatt-hours and, with your rate entered, dollars. We’d start with a per-circuit panel monitor, the only type here that breaks out hardwired and 240V loads circuit by circuit; the table shows what each of the others misses.
The Main Kinds, and What Each Can See
| Type | How It Measures | Sees | Misses |
|---|---|---|---|
| Panel monitor, per circuit | Clamp sensors on the main lines and on chosen circuits | Whole house plus each clamped circuit, including hardwired and 240V loads | Detail on circuits you don’t clamp |
| Panel monitor, device detection | Sensors on the main lines only; software matches electrical signatures to devices | Whole house, plus devices it has learned | Devices it hasn’t learned yet |
| Plug-in meter | Built into a smart plug | One plug-in device | Hardwired and 240V loads, everything else in the house |
| Utility smart meter | The utility’s meter where power enters the house | Whole-house use for billing | Circuits and devices, unless your utility adds software that detects them |
| Solar inverter app | The inverter reports what it produced | Solar production | Household use and grid import or export, unless consumption metering was installed |
How a Panel Monitor Reads Current
Each sensor is a current transformer, a ring that clamps around a wire and reads the alternating current passing through it without touching the conductor. Two larger sensors, rated 200A on both monitors we recommend, go on the main lines where power enters the panel. Smaller ones go on individual circuits: Emporia’s are rated 50A and Refoss’s 60A. Emporia notes its sensors read AC only, so a solar system is measured on the inverter’s AC output.
Emporia lists 24,000 samples per second for the Vue 3; the monitor combines those current readings with voltage to calculate power. Sense, which identified devices by their electrical signatures, analyzed current over a million times a second. Accuracy ratings run plus or minus 2 percent for the Vue 3 and plus or minus 1 percent for the Refoss EM16P.
Per-Circuit Sensors or Device Detection
Per-circuit monitors report what each clamped circuit draws from the first day. If a circuit feeds one appliance, you see that appliance; if it feeds a room’s outlets, you see the room as one number. Device detection tries to name individual appliances from the main-line signal and builds up over time, so it can report less on day one. Sense, a device-detection monitor, ended monitor sales at the end of 2025 and now builds its software into utility smart meters; our Sense vs. Emporia page covers that.
Where the Data Goes
Emporia sends readings to its cloud, which is how its app shows long history and dollar costs. It keeps 1-second data for 3 hours, 1-minute data for 7 days, 15-minute data for a year and hourly and daily data for the life of the device, and shows costs once you enter a rate. If Wi-Fi drops, the Vue 3 holds about 15 minutes of readings and uploads them later. Refoss says the EM16P can operate without the cloud and feeds Home Assistant natively; it also offers free cloud storage of up to 5 years of daily data.
What People Use the Data For
A circuit that never drops to zero points to a load you didn’t know about, such as a second fridge in the garage or a dehumidifier that runs all day. A week of daily watt-hours gives the energy side of battery sizing in our battery sizing guide, and solar owners can check import and export against the utility bill, covered in our solar monitoring guide.
Installation and Safety
Panel monitors install inside the breaker panel with clamp-on sensors; nothing is cut or spliced. The service conductors from the meter stay energized even with the main breaker off, so hire an electrician if you’re not comfortable working in a live panel. Plug-in meters need no installation at all; see our energy monitoring smart plug guide.
Which System to Buy
We’d buy the Emporia Vue 3 with 16 sensors for hourly history kept for the life of the device and costs in dollars in its app, or the Refoss EM16P, also with 16 circuit sensors, for Home Assistant, local data, plus or minus 1% accuracy and a lower price. Our best whole home energy monitors guide compares their warranties, sensor ratings and data retention.
Where This Comes From
Sensor, sampling, data and accuracy details come from Emporia’s help center and store, Refoss’s EM16P product page, and Sense’s help center and product pages, read October 25, 2026. Prices were read on Amazon the same day. Our editorial policy explains how picks are made.