Building a Smart Home System

One of the key principles when designing a smart home is simple: everything in the system must work reliably. If a solution does not provide stable operation, it is better to simplify it or avoid it altogether.

A good example is presence-based lighting automation in a bathroom. Today, there are many motion and presence sensors on the market, and in theory, they seem like the perfect solution.

In practice, however, things are more complicated — especially in households with multiple people and different habits. Presence detection errors occur regularly. If the light turns off while you are still in the bathroom and you have to wave your hand to turn it back on, such automation stops being “smart” and becomes frustrating.

Practical Compromises

If sensor-related issues cannot be fully resolved, it is often better to choose a compromise solution.

For example, automatically turning on the light when entering a bathroom is genuinely convenient, especially if the switch is located inside the room. However, turning the light off manually is often the better option.

This approach eliminates unreliable scenarios and makes the system more predictable.

Decentralization and Fault Tolerance

Wireless smart home systems are inherently more decentralized than wired solutions.

Failure of central equipment — such as a controller or coordinator that handles much of the logic and communication — does not necessarily stop the entire system if it is properly designed. However, it can significantly reduce functionality.

The home remains usable, albeit with limited capabilities.

Reliability Levels

Based on this, we can define three условных levels of reliability for a system or its components:

High reliability means that even if the controller fails, the core function of an element continues to work via a wired connection.

A classic example is a relay installed behind a wall switch, directly connected to a standard switch and a regular light bulb. Pressing the switch will still turn the light on or off regardless of the smart home system state.

Medium reliability assumes operation without a controller, but over a wireless connection.

This is possible when using devices that support binding in Zigbee or Thread networks.

In this scenario, a switch sends commands directly to an actuator — such as a light, curtain motor, or blind controller — bypassing the coordinator.

Low reliability refers to situations where a device completely stops working if the controller fails.

Such solutions are acceptable only for non-critical features where failure does not significantly impact everyday use.

Design Approach

When designing a smart home, it is important to consciously account for these reliability levels.

If the system is planned during new construction or major renovation, electrical wiring should first be designed as if there will be no smart home at all.

Smart devices should then be layered on top of this base infrastructure. This approach significantly improves reliability and provides flexibility for future upgrades.

Ensuring Basic Functionality

Not all devices and scenarios are equally important, but basic functions must always remain available.

Every room should allow at least one lighting group to be controlled independently of the controller.

A popular solution now is using relays from companies like Bosch, Aqara, and Sonoff with a “Decoupled” mode, which separates the physical input from the relay output.

This allows installing the device behind a standard wall switch while using smart bulbs.

When the switch is pressed, a signal is sent to turn lights on or off or trigger a scene via the controller. If the connection is lost, the relay can still directly control the light.

Conclusion

These details are what distinguish a well-designed smart home from a collection of devices that only work under “ideal conditions”.