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Home Automation DISCUSSION
Some of the sensors and plugs I am comparing connect straight to the Wi-Fi router, while others say "requires hub" or "requires gateway" and cost less per device. I would prefer not to buy extra boxes unless there is a technical reason.
Why do hub-based devices exist at all, and what do I gain or lose by building a home automation setup around Wi-Fi devices only?
The hub is a translator between radios. Your router and phone speak Wi-Fi and IP. Many sensors use low-power mesh radios instead: Zigbee and Thread on IEEE 802.15.4 at 2.4 GHz with 250 kbit/s, or Z-Wave in the sub-GHz bands (around 868 MHz in Europe and 908 MHz in North America). Neither your router nor your phone has those radios, so something must sit on both networks and pass messages across. That something is called a hub, gateway, coordinator or border router, depending on the protocol.
So the question becomes why a device maker would choose a radio that needs a translator, and the answer is mostly power.
Wi-Fi is expensive for a battery. Staying associated with an access point means waking regularly for beacons, and a Wi-Fi microcontroller draws tens of milliamps whenever its radio is active, with transmit peaks well above that. A door sensor on Wi-Fi therefore either sleeps deeply and spends a second or more reconnecting for each event, or eats batteries.
An 802.15.4 end device wakes, sends a short frame to its parent and is asleep again within milliseconds, with an average current in the microamp range. That is the difference between a coin cell lasting a couple of years and a pair of AA cells lasting a few months. For mains-powered devices such as plugs and bulbs the argument does not apply, which is why those are commonly Wi-Fi.
Scale and range are the second reason. A mesh network extends itself: every mains-powered Zigbee, Thread or Z-Wave device relays for its neighbours, so adding devices improves coverage. Wi-Fi devices all talk to the access point directly, each one takes an entry in the router's client table, and consumer routers can become unreliable once several dozen clients are associated. Forty Wi-Fi bulbs and plugs is a realistic way to find that limit.
Wi-Fi devices also depend on the 2.4 GHz network settings staying compatible, and many cannot join 5 GHz-only networks or networks with enterprise authentication.
The third aspect is where the logic runs. Many direct Wi-Fi products talk to the manufacturer's cloud, so an automation such as motion turning on a light travels out to a server and back. It stops when the internet connection or the service is down, and the device can lose features if the service is withdrawn. A local hub can run automations inside the house, quickly and with no external dependency.
This is not strictly hub versus Wi-Fi: some Wi-Fi devices offer local APIs or can run open firmware, and Matter devices are controlled locally over IP by design. But it is worth checking for each product whether it keeps working with the internet unplugged.
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