Technology
In our previous guide Smart Home: From Concept to Reality, we explained why and how a smart home based on Home Assistant and Shelly relays works. The most common response we got from our readers was always the same: "That’s all great, but how much exactly does it cost?"
In this article, we give a surgically precise answer. We took a typical 100m² apartment — featuring a living room, kitchen, two bathrooms, a master bedroom, a kids' room, a hallway, and a storage room — and calculated every device, every sensor, every meter of cable. No "ballpark" figures or "roughly". Every item has a specific model, quantity, and price.
Model Apartment: What are we automating?
Our reference apartment has the following structure:
| Room | Area | Light Circuits (Switches) | Roller Shutters/Awnings |
|---|---|---|---|
| Living Room | ~28m² | 3 (ceiling, ambient, LED strip) | 2 |
| Kitchen & Dining | ~16m² | 3 (ceiling, counter, dining) | 1 |
| Master Bedroom | ~16m² | 2 (ceiling, nightstand lamps) | 1 |
| Kids Room | ~14m² | 2 (ceiling, desk light) | 1 |
| Main Bathroom | ~6m² | 2 (ceiling, vanity mirror) | — |
| Guest WC | ~3m² | 1 | 1 |
| Hallway / Entry | ~10m² | 2 | — |
| Storage Room | ~3m² | 1 | — |
| Terrace / Balcony | ~4m² | 1 | 1 (awning) |
| TOTAL | ~100m² | 17 light circuits | 7 motorized shutters |
A. Relays and Dimmers — Lighting & Shutter Control
This is the heart of the system. Every wall switch in the apartment gets a smart relay installed "behind" it — clicking the physical wall switch still works normally, but now the house remembers and reacts.
| Device | Qty. | Price/ea | Total | Purpose |
|---|---|---|---|---|
| Shelly Plus 1PM (Relay with metering) | 10 | €16 | €160 | Basic lighting (ceilings, hallway, storage, terrace) |
| Shelly Dimmer 2 | 3 | €28 | €84 | Ambient lighting (living room, nightstands, dining) |
| Shelly Plus RGBW PM | 2 | €27 | €54 | LED strips (living room cove and kitchen counter) |
| Shelly Plus 2PM | 7 | €22 | €154 | Motorized roller shutters and terrace awning |
| Shelly Plus i4 | 2 | €20 | €40 | Scene controllers behind switches (living & bedroom) |
| Shelly BLU Button1 | 2 | €16 | €22 | Wireless buttons for bedside scene control |
| TOTAL (Section A) | 26 | €514 |
Why Shelly Plus 1PM instead of the standard Plus 1? The "PM" variant measures the energy consumption of each light circuit. At the end of the month, you can check your dashboard and see exactly how much electricity the kitchen lighting used versus the bedroom. The price difference is barely ~€2 per unit — but the data is invaluable.
B. Sensors — The eyes, ears, and nose of a smart home
Without sensors, a house is just a giant remote control for lights. With sensors, it thinks for you.
| Sensor | Qty. | Price/ea | Total | Placement |
|---|---|---|---|---|
| Shelly BLU H&T (Temp/Humidity) | 5 | €18 | €90 | Living room, bedroom, kids room, bathroom, kitchen |
| Shelly BLU Door/Window | 7 | €18 | €126 | Front door + 6 key windows |
| Shelly BLU Motion (PIR) | 3 | €22 | €66 | Hallway, main bathroom, guest WC |
| Aqara FP2 (mmWave radar) | 3 | €50 | €150 | Living room, master bedroom, kids room |
| Shelly Flood Gen4 (Water leak) | 3 | €25 | €75 | Under sink, washing machine, water heater |
| Shelly Plus Smoke (Fire alarm) | 2 | €45 | €90 | Hallway and kitchen (EN 14604 standard) |
| Shelly BLU Gateway | 2 | €15 | €30 | Bluetooth to Wi-Fi bridge (covers the whole apartment) |
| TOTAL (Section B) | 25 | €627 |
PIR vs mmWave: Why combine technologies?
One of the biggest mistakes in smart home design is putting the wrong sensor in the living room.
- PIR (Passive Infrared) sensors: These detect motion (specifically, the movement of a warm body). They are brilliant for transit zones like hallways and bathrooms. But if you sit on the couch to read a book or watch TV, you are not moving enough. The PIR sensor will think the room is empty and turn off your lights. Quite frustrating, isn't it? That is why we restrict them strictly to "transit" zones.
- mmWave (Presence Radar sensors): This is a modern technology that detects actual presence via micro-movements (like human breathing or typing on a phone). The Aqara FP2 costs a bit more (~€50), but the lights in your living room, bedroom, and kids' room will stay on exactly as long as someone is in the room, even if they are perfectly still.
C. Infrastructure — The Brains of the Operation
| Item | Qty. | Price | Notes |
|---|---|---|---|
| Beelink S12 Pro | 1 | €170 | Mini PC (Intel N100, 16GB, 500GB) for Proxmox + Home Assistant. Extremely low power draw (6W). |
| Sonoff ZBDongle-E | 1 | €25 | Zigbee coordinator (necessary for Aqara presence sensors). |
| USB Extension Cable | 1 | €4 | For the Zigbee dongle (prevents USB 3.0 interference). |
| Shelly Pro 3EM | 1 | €110 | 3-phase energy monitor for the entire apartment. Mounts in the main breaker box. |
| Mini UPS | 1 | €45 | Battery backup for the router and mini PC (keeps the system alive during short power outages). |
| Cat6 Ethernet Cable | 1 | €8 | Wired LAN connection from server to router (mandatory). |
| TOTAL (Section C) | €362 |
D. Hidden Costs — What no one writes about
Every project has little details that eventually add up.
- Wago clamps (5-pole): €12 (For safely branching wires inside wall boxes)
- Deeper wall boxes: €35 (Wall boxes need depth to fit the relay behind the switch; standard ones are often too shallow)
- Cable ties & accessories: €10
- Spare batteries: €15 (For BLU sensors)
- USB hub: €12 (For the server, leaves room for additional dongles like Thread/Bluetooth later)
TOTAL (Section D): €84
THE GRAND FINALE: Total Investment
TOTAL: €1,587
E. Optional: Nuki Smart Lock (Keyless Entry)
We did not include a smart lock in the base budget as it is highly subjective, but if you want the ultimate premium experience, we highly recommend the Nuki Smart Lock. It mounts over your existing cylinder on the inside of the door — no drilling required and no locksmith needed.
- Nuki Smart Lock 4.0 Pro: ~€230 (Built-in Wi-Fi and Matter over Thread, rechargeable battery pack)
- Nuki Smart Lock 4.0 (Base): ~€150 (Bluetooth only, requires a bridge or strategically placed ESP32 Bluetooth proxy)
With Nuki, the door automatically unlocks when you approach it with your phone in your pocket (Auto-Unlock). You can remotely let in a handyman or cleaner. Best of all, Home Assistant can automatically arm your home alarm as soon as the Nuki lock secures the door from the outside.
Comparison: How much do alternatives cost?
| System | 100m² Budget | Quality / Reliability |
|---|---|---|
| Shelly + Home Assistant (Our Design) | €1,587 | ★★★★★ (Fully local, extremely flexible) |
| Sonoff + Home Assistant | ~€1,000 | ★★★★☆ (Cheaper hardware, requires more setup/flashing) |
| Tuya / Smart Life | ~€600 | ★★★☆☆ (Cloud-dependent, privacy/security risks) |
| KNX (Wired standard) | €15,000 – €30,000+ | ★★★★★ (Industrial premium standard) |
| Loxone | €8,000 – €15,000 | ★★★★★ (Excellent professional system) |
| Control4 / Crestron | €20,000 – €50,000+ | ★★★★★ (Ultra-premium, custom solutions) |
Time Investment: How many weekends do you need?
If you are taking the DIY approach, here are realistic estimates:
- Relay Installation (26 devices): 5-6 hours for experienced / 10-12 hours for beginners. (Always turn off the breakers!)
- Sensor Mounting (25 devices): 2 hours for experienced / 4 hours for beginners. (Most use double-sided tape).
- Proxmox + HA Installation: 30 minutes to 2 hours.
- Network Onboarding: 2 to 4 hours.
- Creating Automations: 3 to 6 hours for the core 15-20 rules.
- Dashboard Design: 4 to 8+ hours (this is usually an enjoyable endless rabbit hole).
Total: 16 to 30 labor hours. This breaks down to one serious weekend or up to three relaxed weekends of work.
ROI: Return on Investment
A smart home isn't just a comfort gadget — it returns the money invested through savings:
- Zonal HVAC control + automated lighting shutdown + eliminating "standby" power: savings of €260 to €450 annually.
- Total Investment: €1,587 (without Nuki lock)
- Payback Period: ~3.5 to 6 years (conservative estimate). With active HVAC optimization, the investment pays for itself in 2.5 to 3.5 years.
Phased Approach: You don't have to buy everything at once
Sometimes it is best to start slow. Here is our recommended 4-phase plan:
- Phase 1 — The Foundation (€370): Mini PC + Home Assistant + 5 basic relays + 2 PIR motion sensors + 1 BLU Gateway + Zigbee dongle + cables. (Result: The system is alive, hallway/bathroom lights work automatically).
- Phase 2 — Safety & Sensors (€380): 3 flood sensors + 2 smoke alarms + 5 H&T + 4 window sensors + 3 mmWave sensors. (Result: The apartment is secure, reacting to climate and presence).
- Phase 3 — Lighting & Ambience (€380): The remaining 5 relays + 3 dimmers + 2 RGBW + 2 smart switches (i4) + 2 bedside BLU buttons + 3 window sensors + 1 more BLU Gateway + deeper boxes. (Result: Complete lighting magic and scenes).
- Phase 4 — Shutters & Monitoring (€457): 7 shutter modules (Plus 2PM) + Pro 3EM (electricity) + mini UPS + remaining miscellaneous items. (Result: Absolute integration of everything).
Conclusion
For roughly €1,587, you can build a system that rivals €20,000 professional solutions. The combination of Shelly devices, Aqara sensors, and Home Assistant offers an unbeatable balance of quality, cost, and freedom (local control, no subscriptions).
If you feel this is too challenging, or simply do not have the time for wiring and programming, feel free to contact us for professional planning and installation.