MTN Weekend: How to build a smart home that still works when the internet goes down
A locally controlled smart home can keep essential devices and automations running when the internet connection fails. Photo: Rafael Garcin/Unsplash.
On 18 August, Google Home users reported that speakers, displays and routines had stopped responding. Some Nest Hub screens became stuck, while voice commands and household automations failed. The devices had not suddenly broken. A server-side disruption had separated them from the cloud services they needed to operate.
It exposed a weakness built into much of the smart home. A command to switch on a light may leave the house, travel to a manufacturer’s server and return before reaching a bulb in the next room. If the broadband connection or cloud platform fails, the house loses part of its intelligence.
A smart home can work without the internet if its controller, automations and devices communicate locally. Home Assistant combined with Zigbee is one of the most accessible ways to build one. Cloud-only devices and most online voice assistants will stop working until the connection returns.
For around €250, beginners can build a basic offline smart home in an afternoon without writing code.
| Beginner smart-home build | Estimate |
|---|---|
| Approximate cost | €220–€270, excluding optional UPS |
| Setup time | One to two hours |
| Difficulty | Beginner-friendly |
| Coding required | No |
| Works without internet | Local controls, sensors and automations |
| Still needs internet | Remote access, most online voice assistants and cloud-only devices |
Prices vary between retailers and marketplace sellers.
Step 1: Set up Home Assistant for local control
Every smart home needs a central controller. In cloud-dependent systems, much of that controlling intelligence lives on a manufacturer’s servers. In this build, it runs on a small computer inside the home.
One of the most established platforms for doing this is Home Assistant, an open-source system overseen by the Open Home Foundation. It stores dashboards, automations and device information locally and can communicate directly with compatible products.
The easiest entry point is Home Assistant Green, available through many specialist retailers. Home Assistant is already installed, so there is no operating system to configure.
Connect Home Assistant Green to the router with the supplied Ethernet cable, attach its power supply and wait for it to start. The accompanying app or a web browser will guide the user through creating a local Home Assistant installation.
The controller does not need the internet to run established local automations, but it does need a functioning home network. If the router itself stops working, devices that depend on that network may no longer reach the controller.
As MTN has previously explored, cloud dependence creates another risk: connected products can lose important functions when a manufacturer withdraws the service behind them.
Step 2: Add a Zigbee radio
Home Assistant Green does not have a built-in Zigbee radio. To communicate with Zigbee plugs, sensors and buttons, it needs a separate coordinator.
Home Assistant recommends the Connect ZBT-2 for new Zigbee installations. Plug it into Home Assistant Green and select Zigbee during the setup process. The same adapter can instead operate as a Thread radio, but it cannot run Zigbee and Thread simultaneously.
Zigbee is a low-power wireless technology created for connected devices including bulbs, plugs, switches and motion sensors. It establishes its own mesh network rather than placing every product directly on the home Wi-Fi.
Permanently powered Zigbee devices, such as smart plugs, can pass messages between other devices. Adding several around a house may therefore improve the network’s coverage. Battery-powered products such as buttons and motion sensors generally communicate through the mesh without relaying other traffic.
Products from different manufacturers can share a Zigbee network, but compatibility is not guaranteed. Home Assistant warns that some devices do not implement every part of the standard correctly. Check the exact model before buying rather than relying solely on the Zigbee logo.
Step 3: Pair the plug, sensor and button
Begin with one room rather than trying to automate the entire house.
A useful starter system needs three devices:
- a Zigbee smart plug connected to a lamp;
- a Zigbee motion sensor; and
- a Zigbee wireless button.
For this build, MTN selected Sonoff devices because the company offers all three product types and supplies firmware updates through Home Assistant’s Zigbee Home Automation integration.
Sonoff states that its SNZB-03P motion sensor works with Home Assistant through either Zigbee2MQTT or the platform’s ZHA integration. Some ZHA installations may require an additional device handler or script, however, so check the latest instructions for the exact model before pairing it.
In Home Assistant, open Settings, select Devices & services and enter the Zigbee integration. Choose the option to add a device, then put each accessory into pairing mode according to its instructions.
Give the devices clear names such as “Hall motion sensor”, “Hall lamp” and “Hall button”. Sensible names become increasingly helpful once a system expands beyond its first room.
Pair and test each product before adding the next. This makes it easier to identify the cause if something fails to appear.
Step 4: Create the first local automation
The first automation can be extremely simple:
When the motion sensor detects someone in the hall after sunset, switch on the lamp. When no movement has been detected for several minutes, switch it off.
Home Assistant includes a visual automation editor, so no programming is required. Select the motion sensor as the trigger and the smart plug as the action. A sun condition can prevent the lamp switching on unnecessarily during daylight.
Configure the wireless button separately so that pressing it toggles the same lamp. It provides physical control when someone does not have a phone or simply does not want to open an app.
This illustrates the difference between remote control and automation. Replacing a wall switch with a smartphone screen only relocates the switch. A useful smart home can respond to movement, time, temperature or light levels while still allowing the people inside it to intervene.
Because the sensor, controller, button and plug communicate locally over Zigbee, the automation does not have to contact Sonoff’s cloud or any other external server before operating.
Step 5: Disconnect the internet and test it
Do not wait for an actual outage to discover which products quietly depend on the cloud.
Disconnect the incoming internet cable from the router while leaving the router powered. This removes access to the wider internet but keeps the Wi-Fi and local home network running.
Now test the system:
- Walk past the sensor. Does the lamp switch on?
- Press the wireless button. Does the plug respond?
- Can a phone connected to the home Wi-Fi still open the Home Assistant dashboard?
- Do existing heating schedules continue?
- Can locally managed cameras still record?
- Which apps or devices report errors?
Home Assistant can continue operating without an internet connection. Devices using local technologies including Zigbee, Z-Wave, Matter, Thread and ESPHome should also remain available. Cloud-only devices, remote access from outside the home and most connections to Amazon Alexa or Google Assistant will not.
The test distinguishes products that merely connect to the local network from those that can actually be controlled through it.
Which smart-home devices work without the internet?
An internet outage, a failed router and a power cut are three different events. A locally controlled system handles the first, but does not automatically solve the other two.
| Smart-home function | Internet down, local network working | Power down without backup |
|---|---|---|
| Local Zigbee automations | Yes | No |
| Zigbee wireless button | Yes | Button remains powered, but controller and plug are offline |
| Home Assistant dashboard over home Wi-Fi | Yes | No |
| Alexa or Google Assistant | Usually no | No |
| Remote access from outside | No | No |
| Battery-powered sensors | Yes | Remain powered, but cannot reach an unpowered controller |
| Router and controller connected to a UPS | Yes | Temporarily |
| Ordinary mains-powered lights and plugs | Yes | No |
A small uninterruptible power supply, or UPS, can keep Home Assistant Green, the router and the Zigbee coordinator operating during a brief power interruption. It will not power the rest of the house.
Check the UPS capacity, socket type and estimated runtime before purchasing. A unit intended for a desktop computer may be unnecessarily large, while a very small backup supply may not support both the controller and network equipment.
Where Matter and Thread fit
Readers buying new smart-home products will increasingly encounter Matter and Thread alongside Zigbee.
Matter is an interoperability standard supported by major technology companies including Apple, Amazon, Google and Samsung. Matter devices are designed to allow local control without requiring a manufacturer’s cloud for routine operation.
However, this does not mean every Matter product is entirely cloud-free. Some manufacturers still require an account or proprietary app for initial setup, firmware updates or additional features.
Thread is a low-power mesh networking technology over which some Matter devices communicate. Other Matter products use Wi-Fi or Ethernet. A Thread device requires a Thread border router, which may already be built into a compatible smart speaker or hub.
Matter is attractive for future expansion, but Zigbee currently offers a mature and relatively affordable starting point. The Matter logo should not be mistaken for a guarantee of effortless installation: some products and platform combinations have experienced pairing and connectivity problems.
Keep a manual way out
Automation should add convenience without removing basic control.
A wireless button is often more practical than expecting everyone to use an app. Heating needs a safe fallback, a smart lock should retain a key or keypad, and essential lights should remain operable if the controller is unavailable.
Take particular care with locks, garage doors, ovens and equipment whose unexpected behaviour could create a safety or security problem. A first automation should involve something forgiving, such as a table lamp, rather than the front door.
Running the controller locally also gives the homeowner more responsibility. Install security updates, use a strong password and never expose the Home Assistant interface directly to the public internet without an appropriately secured remote-access method.
Create regular backups as well. Home Assistant can produce encrypted backup archives containing its configuration, database and selected add-ons. Store a copy away from the controller so that a failed storage device does not erase the entire setup.
Readers interested in keeping more of their data on hardware they control can also explore our article about How to build a private AI that never talks to the cloud.
The cloud becomes an addition, not the foundation
Cloud services remain useful. They provide remote access, weather information, notifications away from home and powerful online voice assistants. The crucial choice is whether the internet adds these capabilities or whether every light and sensor depends on it.
Local-first smart homes are also moving beyond the enthusiast community. At IFA 2026, Ugreen introduced HomeAgent, a platform combining smart-home control, locally stored security footage and on-device AI. Its principal functions are intended to operate offline, although remote viewing and external notifications still require an internet connection.
A genuinely smart home does not need to cut itself off from the outside world. It needs to know which decisions it can make for itself.
The simplest way to find out is to pull the internet cable. If almost nothing changes, the intelligence was in the house all along.
What you need for this beginner build
This section contains affiliate links. MTN may receive a commission from qualifying purchases at no additional cost to the buyer.
- Home Assistant Green – the local controller
- Home Assistant Connect ZBT-2– the Zigbee coordinator
- SONOFF S60ZBTPF Zigbee Smart Plug controls the lamp and helps extend the Zigbee mesh
- Sonoff SNZB-03P motion sensor – detects movement
- Sonoff SNZB-01P wireless button at bol.com – provides physical control
- Compact UPS – optional protection against brief power interruptions
A more configurable alternative
Technically confident readers can run Home Assistant on a Raspberry Pi 5. The board also requires a compatible power supply, storage, a case and active cooling, so it is not necessarily cheaper or easier than Home Assistant Green.
Prices, availability and marketplace sellers can change. Check the exact model, seller, electrical specifications and current Home Assistant compatibility before buying.
Frequently asked questions
Does Home Assistant work without the Internet?
Yes. Home Assistant runs on hardware inside the home. Local integrations and automations can continue working when the external internet connection is unavailable, provided the controller, router and relevant devices still have power.
Does Zigbee work without Wi-FI?
Yes. Zigbee creates a separate wireless mesh network. Home Assistant still needs to communicate with its Zigbee coordinator, while phones accessing the Home Assistant dashboard generally use the home Wi-Fi or a wired connection.
Does Matter work without the internet?
Matter supports local device control. However, some manufacturers still require an online account or proprietary app for initial setup, updates or optional features.
Will Alexa or Google Assistant work during an internet outage?
Most Alexa and Google Assistant voice functions rely on cloud processing and may become unavailable. Locally executed automations and physical Zigbee buttons offer more reliable fallbacks.
Will a smart home work during a power cut?
Not unless its essential components have backup power. A UPS can temporarily power the controller and router, but ordinary mains-powered lights and appliances will remain unavailable.
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