Buying
Retrofit smart locks turn the thumbturn you already have. Nothing is drilled, the cylinder stays, the key still works, and the door goes back as it was. What they change is who can open it and when — and not, in any respect, how hard it is to force.
There are two products called a smart lock and only one of them suits a tenant.
A retrofit mounts on the inside and turns your existing thumbturn. A replacement takes over the cylinder itself, which a tenancy rarely permits and which changes the key everybody holds.
A thumbturn on the inside, with clearance around it. Doors keyed on both sides need a thumbturn cylinder first — which costs a fraction of the lock and is itself a change to ask about.
An open protocol. A lock speaking Matter joins Apple Home, Google Home or Alexa directly and does not depend on one company continuing to run a service. On a device you keep for years, that matters more than the number of unlocking methods.
It is convenience and control. Not resistance.
Retrofit · fingerprint, app and Bluetooth · magnetic auto-lock · 6 cells · no drilling
A retrofit lock that mounts over an existing cylinder with no drilling and no cylinder change. Signstek states fingerprint, app and Bluetooth access, magnetic auto-locking, and six batteries; the existing key still works from outside.
Best for: A first smart lock, and particularly a rented flat where nothing may be altered.
≈ 130 €
Matter over Thread · Apple Home Key · rechargeable Li-ion, 6 months stated · no drilling
A retrofit lock with native Matter over Thread, so it joins Apple Home, Google Home and Alexa without a vendor bridge. Aqara states Apple Home Key support, a rechargeable battery quoted at up to six months, and a quiet unlocking mode.
Best for: A household already running Matter or Apple Home, that wants the lock to be part of it rather than another app.
≈ £200 / 170 €
Retrofit · built-in Wi-Fi, no bridge · Matter · charged at the door · months per charge
Nuki's fifth-generation lock puts Wi-Fi inside the unit, so remote access needs no bridge or hub, and adds Matter alongside Bluetooth. The battery charges at the door with the supplied cable rather than coming off it.
Best for: A household that wants remote access without adding another box to the hallway.
≈ £189 / 233 €
No. It turns the thumbturn. The cylinder, the strike plate and the frame are exactly as they were, and those are what resist force. If the door is the weak point, the money belongs in a cylinder and long screws rather than here.
Your key still opens the door, because the cylinder was never touched. That is the structural advantage of retrofit locks over replacement ones — and it only helps if the key is somewhere other than inside the locked flat.
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