Smart Home in a Power Cut
What Fails, What Survives & How It Restarts

What a blackout does to a smart home

When TNB supply drops, every device in the house falls into one of three groups within a second. Devices on the house supply with no battery simply stop. Devices with their own battery carry on but lose the network around them. Devices plugged into a backup supply keep running as if nothing happened, for as long as that backup lasts.

The second group is where people get confused. A battery door sensor still notices the door open, but the hub it reports to is off, so the message goes nowhere. A battery lock still opens with a PIN, but the app on your phone cannot reach it. The house is half awake, and nothing joins the halves together until the power comes back.

Fail safe or fail secure: decide before the outage

For every device that controls something physical, ask one question: when the power fails, what should this be doing? The answer is not always the same, and it should be a choice rather than an accident.

• Doors and locks: make sure there is always a way out from inside and a way in from outside. The smart lock battery and power-failure guide covers the override key and emergency power point.
• Gates: an autogate stops with the supply unless its own battery takes over. The autogate power-cut guide explains the manual release.
• Water valves on a leak system: know whether the valve stays where it was or moves, and how to turn it by hand.
• Curtains and blinds: a battery motor keeps working; a mains motor stops where it is, which matters for a bedroom that must be dark or a window that must close in a storm. The battery versus wired curtain motor guide compares the two.
• Water heater and pump timers: these should come back off, not on, after an outage.

Which boxes are worth backing up

An uninterruptible power supply is an electrical apparatus that provides emergency power to a load when the mains fails, as Wikipedia describes it. In a smart home you do not need to back up everything. You need the handful of boxes that hold the network together, because they decide whether the battery devices can still reach you.

How big the backup should be and which type to buy is a separate question, answered in the home UPS guide for routers and CCTV. The point here is the list: if the fibre modem, the router and the hub sit in three different rooms, one backup unit cannot cover them, and moving them to one spot is often the real job. Any mains electrical work, such as a new power point, a change at the distribution board or a hardwired switch that needs new wiring, must be done by an electrical contractor registered with Suruhanjaya Tenaga.

Power-on state: what plugs and relays do when the supply returns

Most smart plugs and many relays have a setting, usually found in the device's options in the app, that decides what happens when power comes back: always off, always on, or return to the last state. Out of the box it is often set to off or to the last state, and few people ever look at it.

Go through the list once and set each one deliberately. A fridge or a fish-tank pump on a smart plug should come back on. A heater, an iron, a kettle or anything that should never run unattended should come back off. The smart water heater timer guide explains why a water heater should not restart on its own. Write the settings down; a factory reset or a firmware update can put them back to the default.

The order things come back

When the supply returns, every box restarts at once, but they are not equally quick. The router is often slower than the plugs and bulbs that join it, so WiFi devices try to reconnect, fail and wait. A hub that comes up before the router may not reach the cloud for a while. Most systems sort themselves out, but a few devices stay offline until someone restarts them.

1. Wait until the fibre modem shows a steady connection.
2. Check that the router and any mesh nodes are back and the WiFi name is visible.
3. Open the hub's app and see which devices show as offline.
4. Restart only the devices that are still offline, by switching them off and on again at the plug or by re-inserting the battery.
5. Run one or two key scenes, such as the corridor lights, to confirm the hub is in control again.

If the same devices go missing after every outage, they are telling you something. Zigbee battery sensors that lose their parent router may not find a new one, a problem the guide to Zigbee range and repeaters deals with in detail.

Automations that misfire after the power returns

Automations assume the house has been running all along. After an outage that assumption breaks, and the results can be odd: the porch light that should have come on at dusk stays off because the hub missed the moment, or a motion rule fires in an empty room as every sensor reports in at once.

• Prefer rules that check a condition, such as "after sunset and before midnight", over rules that rely on one exact moment.
• Add a short wait after the hub starts before any rule that switches heavy loads.
• Make sure no rule switches the water heater, the pump or the aircon on just because the hub restarted.
• Look at the hub's history after the next outage to see which rules ran and why.

Sensors and alarms in the dark

A blackout is exactly when people want their security to work, and exactly when a smart-home alarm built on WiFi and the cloud is weakest. Battery sensors keep sensing, but the alert has to travel through the hub, the router and the internet, all of which are off unless backed up.

If security matters, back up the hub and the network as described above, and choose a siren or alarm panel with its own battery so the house can still make a noise locally. Water leak sensors are in the same position: the water leak sensor guide explains how local alarms and valves behave.

Flickers, brownouts and repeated trips

Not every outage is a clean cut. A storm can bring short flickers or a supply that dips without failing, and smart devices dislike both. Each flicker is a small restart, and some cheap devices lose their settings or need re-pairing after several in a row. Backup power on the network boxes smooths this out for the parts that matter most.

If the house itself trips repeatedly, the cause is in the electrical installation, not the smart home. The power tripping guide explains how to narrow it down, and adding more smart devices to a circuit that trips will not fix it.

A blackout drill for the household

A planned test on a calm afternoon teaches you more than any guide. Agree the steps with the family first, especially anyone elderly or a helper who is often home alone.

1. Note the time, then switch off the main switch at the distribution board, or wait for the next real outage.
2. Try the front door lock, the gate, a door sensor and the alarm siren, and note what works.
3. Check whether the router and hub stayed on, if they are on backup power.
4. Switch the supply back on and time how long the internet and the hub take to recover.
5. Walk the house and list every device that is offline or in the wrong state.
6. Fix the power-on settings and the problem devices, then repeat the test another day.

If an outage happens while the internet is fine but your smart home still misbehaves, the problem is a different one: the guide to local control without internet covers it.

How ClickBina helps

We walk through your setup with you and mark what each device does when the power fails and when it returns. We set the power-on behaviour of plugs and relays, adjust the automations that misfire, group the router, hub and recorder where one backup unit can serve them, and re-pair the sensors that go missing after an outage. We do the smart device, app and low-voltage side of the job.

For smart switches and anything wired into the mains, we supply the devices and set up the app, and the switch or wiring work is done by an electrical contractor registered with Suruhanjaya Tenaga that we coordinate. Keep a printed copy of the restart steps somewhere easy to find, and make sure the hub and router accounts are in your own name.

Sources & references

• Wikipedia: Uninterruptible power supply: what a UPS does when the mains fails.
• Zigbee2MQTT: Zigbee network: end devices lose traffic when their parent router goes offline.
• Each device's app and manual: the power-on state setting and how the device behaves after an outage.

This page is general guidance on smart homes during power cuts. Electrical faults and new power points are a matter for a registered electrical contractor, as noted above.