When the conversation comes to the "Smart Home", the average person imagines touchscreens, futuristic switches that glow and, of course, dust, digging and expensive electricians.
This image belongs to the past. The biggest technological breakthrough for existing homes in Europe came in small, colorful boxes no bigger than a matchbox. These are Smart Relays (Micro-Modules). Companies such as European Shelly, Sonoff and Fibaro have completely changed the rules of the game, allowing owners to "hide" technology within their walls.
As engineers, we consider micro-modules the ultimate "Retrofit" solution. Let's take a look at exactly what they are, how they work and why they save your renovation budget (and aesthetics).
A smart relay is essentially a tiny electronically controlled switch (relay) integrated together with a Wi-Fi (or Zigbee/Z-Wave) board.
It is installed exclusively flush, inside the plastic wall box, right behind your old, mechanical switch. Its purpose is to take control of the lamp, but without removing the switch that you press with your hand.
In a simple, traditional wall, current flows through the switch: You press the button, the iron closes the circuit, current goes to the lamp.
When the electrician installs a smart relay (eg a Shelly 1), the architecture changes:
What does this mean in practice? The wall switch no longer controls 230V current for the lamp. It simply sends an electronic signal (command) to the relay. The relay "understands" that you pressed the button, and in turn lets current pass to the bulb.
This gives you Dual Control: You can turn the light on from your mobile, then turn it off from the wall switch, without one canceling out the other!
The advantages of this approach are impressive:
This is the most important thing. You keep exactly the same switches (eg the Legrand Valena or Vimar Plana series you have throughout the house). No change in aesthetics. A visitor will never know that the house is smart until you show them.
If the Wi-Fi goes down, or if your central Server crashes, you are not left in the dark. You press the physical switch and the relay (on almost all models) executes the command locally.
No need to dig up walls. Installation takes 10 minutes per switch, and the cost of a relay (such as the Shelly Plus 1 Mini) is often no more than €15 - €18.
They come in different variations. Some measure energy consumption, others control electric roller shutters and others dim the lights.
If there is one and only problem with smart relays, it is their physical (spatial) placement.
Behind your switch is the plastic box. The old, round "barrels" (boxes) in Greek houses of the '80s and '90s, are usually 40 millimeters (40mm) deep. When you try to fit the switch mechanism, thick wires (1.5mm²) and a relay into such a small space, it becomes suffocating.
The solution for modern renovations: If you are renovating and changing pipes, ask your electrician to put in a box with a depth of 50mm or 60mm. This extra 1-2 cm makes installing smart relays a breeze, offering plenty of space for proper and safe wiring. (Alternatively, companies like Shelly have recently brought out their "Mini" range, which is 35% smaller precisely to solve this European problem).
Micro-Modules brought automation to the masses. They are the most "painless", stylish and economical way to bring a twenty-year-old home into the 21st century, keeping the classic feel of the switch (the classic "clack") and adding the intelligence of mobile and voice assistants.
Next Step: Having now learned about the hidden Smart Relays (Micro-Modules), it's time for the big decision. Keep the old switches and put relays behind them, or rip them all out and buy brand new flat "Smart Switches" with touchscreens?
We continue to the next, practical comparison guide: Smart Switches vs. Smart Relays: Comparison of cost, ease of installation and reliability.
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