The first step to eliminating physical keys from your Airbnb is choosing the right hardware. But with so many options on the market, it's easy to get confused. Nuki, Shelly, and Fermax are the three solutions that keep coming up in conversations among European vacation rental hosts — and for good reason. Each one excels in a different scenario.
What to look for in a smart lock for vacation rentals
Before comparing brands, it's worth defining what matters most in a rental context. Unlike a private home, a vacation rental has specific requirements:
- Remote access: you need to control and check the lock without being physically present.
- Time-limited codes or links: access should expire automatically at checkout.
- No app required for guests: guests shouldn't need to download anything or create an account.
- Audit log: know who opened the door and when.
- Reliability: if the lock fails, guests are locked out — there's no margin for error.
- Easy installation: ideally something you can set up yourself without a locksmith.
Nuki — The retrofit king
Nuki is an Austrian brand and one of the most mature smart lock ecosystems in Europe. Its flagship product, the Nuki Smart Lock, attaches to the inside of your existing door, fitting over your existing thumb-turn cylinder. This means no locksmith, no new keys cut, no drilling.
Nuki works via Bluetooth by default, giving access from a phone within range. Add the Nuki Bridge (sold separately) and you get full remote access over WiFi — essential for vacation rentals.
- ✓ Installs in minutes over your existing cylinder — no locksmith needed.
- ✓ Works with the vast majority of European mortise locks.
- ✓ Excellent app with time-limited access codes and auto-unlock.
- ✓ Supports keypad, fob, and app access.
- ✓ Detailed access logs.
- ✓ Strong integrations (Airbnb, Booking.com, HomeKit, Alexa).
- ✗ Remote access requires the Nuki Bridge, sold separately (~€60–80).
- ✗ Higher upfront cost vs. Shelly (~€150–200 for lock + bridge).
- ✗ Battery-powered: needs regular replacement (every 3–6 months with heavy use).
- ✗ Doesn't solve building entry — only the apartment door.
Best for: Properties with a standard European cylinder lock where you want a clean, reliable retrofit with minimal technical setup.
Shelly — The flexible, budget-friendly option
Shelly is a Bulgarian IoT brand best known for its cheap, powerful smart relay modules. Unlike Nuki, Shelly doesn't make a traditional door lock. Instead, its devices control existing electric releases — the kind already found in many apartment building entry doors and intercom buzzers.
The most relevant product is the Shelly 1 or Shelly Plus 1, a WiFi relay that you wire in parallel with your existing electric door release. When triggered via app, webhook, or API, it briefly closes the circuit and opens the door — exactly like pressing the button on your intercom.
- ✓ Extremely affordable (€10–20 per device).
- ✓ Works with any electric door release or buzzer — no lock replacement needed.
- ✓ Full REST API and webhook support — integrates with any platform.
- ✓ No subscription fees; cloud optional (can run fully local).
- ✓ Shelly Gen 2/3 devices are highly reliable and well-supported.
- ✗ Requires some technical knowledge to wire and configure.
- ✗ No native access log or time-limited codes out of the box (needs external automation or a platform like Colibree).
- ✗ Not a replacement for the apartment door lock — only controls electric releases.
- ✗ Guest experience depends on how you expose the control (app link, webhook, etc.).
Best for: Technically comfortable hosts who want the cheapest possible solution, or those who need to control a building intercom buzzer rather than the apartment door lock directly.
Fermax — The intercom specialist
Fermax is a Spanish brand with decades of experience in building intercom and door entry systems. You'll find Fermax hardware in thousands of apartment buildings across Spain, Portugal, and Latin America.
Its most relevant offering for vacation rental hosts is the Fermax Loft or Fermax VEO series — smart video intercoms with app connectivity. With these, you can answer the door from your phone and remotely open the building entry, with no need to be physically present.
- ✓ Excellent fit if your building already has Fermax intercom infrastructure.
- ✓ Smooth video intercom experience with remote door opening.
- ✓ Well-supported in Spain with a strong local installer network.
- ✓ Some models support virtual keys and temporary access.
- ✗ Primarily solves building entry, not the apartment door lock.
- ✗ Usually requires professional installation.
- ✗ Higher cost when installing from scratch.
- ✗ Less flexible API compared to Shelly; tighter ecosystem.
Best for: Hosts in Spanish (or Latin American) apartment buildings that already have Fermax intercom infrastructure and want to add remote door opening without replacing the whole system.
Quick comparison
- Nuki — Best all-round smart lock for the apartment door. Plug-and-play, great app, solid ecosystem. The go-to for most Airbnb hosts.
- Shelly — Best budget option for electric door releases and intercoms. Requires technical setup but offers unbeatable flexibility and price.
- Fermax — Best for Spanish apartment buildings with existing Fermax intercom infrastructure.
Can you combine them?
Absolutely — and many hosts do. A common setup in Spain is: Fermax (or Shelly) for the building entry buzzer, plus Nuki for the apartment door itself. This gives guests a seamless two-step entry entirely from their phone, with no physical keys at any point.
The piece most hosts overlook
Whichever hardware you choose, the smart lock is only half the solution. The other half is knowing that the person using it has the right to be there.
This is where many hosts stop short: they set up a smart lock system, but guests receive access links without any prior identity verification or signed rental contract. If something goes wrong, there's no paper trail.
Colibree Rentals Manager integrates with your smart locks and adds the missing layer: digital contracts with remote signing, before access is granted. The flow is: guests sign the contract → you approve → you generate the access link and send it. Whether you're using Nuki, Shelly, or Fermax, the access management layer stays the same.
If you work with a team, you can delegate the task of generating and sending access links to a co-host or assistant — with role-based permissions that keep contracts and sensitive information visible only to those who need it.
Conclusion
There's no single "best" smart lock for Airbnb — it depends on your setup. Nuki wins on ease and ecosystem; Shelly wins on price and flexibility; Fermax wins if your building already uses it. In many cases, the best setup combines two of them.
What they all have in common: they're hardware. The workflow around them — who gets access, when, and on what terms — is what Colibree Rentals Manager handles. Sign in with Google and set up your first property in minutes.