How much power a smart home draws
What a local-first Home Assistant setup draws, where the watts hide, and how to pick efficient gear without chasing meaningless savings.
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Building a local-first smart home with Home Assistant keeps your control and your data at home. It also means you’re running hardware 24/7, so it’s fair to ask what that costs. The answer: a sensible local-first setup draws very little, the biggest variable is what you run Home Assistant on, and chasing the absolute lowest wattage usually costs you more in reliability than you save on the meter.
Know your power draw: the hub matters most
Your always-on hub is the thing that runs every hour of every day, so its idle draw dominates. A Raspberry Pi 4 running Home Assistant idles in roughly the 3-5 W range; purpose-built appliances like the Home Assistant Green and the Home Assistant Yellow (discontinued in October 2025, but fine if you already own one) are in the same low-single-digit-watt territory. Over a year that is real but small: 3-5 W works out to roughly 25-45 kWh, a few dollars at typical US rates.
Step up to a small x86 box (a mini PC or NUC-class machine) and idle draw is typically more like 6-12 W, climbing higher under load. That’s still modest, and the extra headroom is often worth it if you run add-ons like Frigate for camera object detection. Neither one is the “right” answer; the hub is where the steady watts live, not your sensors.
Radios sip power. A Zigbee coordinator like the SONOFF Zigbee 3.0 USB Dongle Plus or a Z-Wave controller such as the Z-Wave.Me RaZberry 7 Pro draws a fraction of a watt - negligible next to the host.
A note on ecosystems: if you also use Apple Home, the Apple HomePod mini or Apple HomePod 2nd Gen act as Thread border routers and speakers, but they’re full-time appliances with speaker-class draw, not a low-power “hub” replacement for Home Assistant. They’re not Z-Wave controllers, either - different job entirely.
Battery vs. mains sensors
For most sensors, battery life is the meaningful question, not grid watts. Battery-powered low-power sensors like the Aqara Door/Window Sensor P2 and Aqara Motion Sensor P2 (both Matter-over-Thread) draw so little that they run for months to years on one set of lithium cells - a CR123A in the Door/Window P2, two CR2450 coin cells in the Motion P2 - and they cost you nothing on the meter. Their “efficiency” is about how often they have to wake and report.
Mains-powered devices are where standby draw adds up across many units. Always-on Wi-Fi plugs, relays, and bulbs each pull a small amount continuously. None of it is large per device, but it scales with device count, so favor efficient gear where you’re deploying many.
Choose efficient devices without overthinking it
For controllable outlets, a metering plug - whether a Zigbee/Z-Wave plug or a Wi-Fi unit like the Shelly Plug US Gen4 - lets you measure what appliances actually use, which is more valuable than guessing. For lighting, LED smart bulbs such as the Philips Hue White A19 or LIFX A19 Color are already low-wattage when on; the bigger savings come from automating them off, not from spec-sheet hunting.
For locks, be accurate about what you are buying. The Yale Assure Lock 2 is battery-powered and offered with swappable connectivity modules (Wi-Fi, Z-Wave, Matter), so it does not add to your grid draw at all. The Yale Assure Lock 2 Plus runs on batteries too, but it is the Apple Home Key model and does not take those modules - Home Assistant reaches it locally over Bluetooth instead. The Kwikset Halo Touch is a Wi-Fi lock (2.4 GHz, no hub required) - not a Z-Wave lock, and not something a HomePod controls. Pick the connectivity that matches your stack; the battery does the work either way.
For a Matter relay, the Sonoff MINIR4M is a low-draw Wi-Fi Matter device. As with any always-on Wi-Fi unit, its standby cost is small but real per device.
Don’t over-optimize for power saving
Here’s the tradeoff worth internalizing: the watts you’d save by buying the cheapest, lowest-power gear are usually trivial compared to the cost of an unreliable system. A flaky sensor that misses events or a hub that can’t keep up will cost you far more in frustration than the wattage difference ever saves in dollars.
Run Home Assistant on hardware sized for what you actually do. Here is how to build a low-power Home Assistant server. If you’re doing local camera AI, a mini PC’s extra idle watts buy you capability a Pi can’t match. If you’re running lights and sensors, a Green or a Pi is plenty. Either way, the radios and battery sensors are rounding error.
Bottom line: be realistic
A local-first Home Assistant setup is inherently efficient - the steady draw is your always-on host (a few watts on a Pi/Green, more on an x86 box), and almost everything else is negligible or battery-powered. Use a metering plug to find your actual energy hogs (usually appliances, not smart-home gear) - see the best local smart plugs with energy monitoring - automate things off when they’re not needed, and right-size your hub for your workload.