The interesting question is what happens when the battery dies · review
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.
The bottom line The cheap way in, and the honest way to describe it is convenience rather than security. For a tenant it is the only option in this hub.
There are two kinds of product called a smart lock, and confusing them is the commonest mistake in this family.
A retrofit. It mounts on the inside of your door and turns the thumbturn you already have. Nothing is drilled, the cylinder is not replaced, and the door can be returned to its original state — which is why this is the only kind of smart lock a tenant can normally fit.
Your door’s resistance to force. The cylinder is the same cylinder, the strike plate is the same strike plate, and the frame is the same frame. A retrofit lock changes who can open the door and when; it does not change how hard it is to break. Anybody selling it as an upgrade to security is selling the wrong story.
If you want the door itself to resist better, the cylinders and door bars in the neighbouring hubs are where that money goes.
Six cells, and Signstek does not publish the daily cycle count behind any runtime figure, so we do not convert it. What matters more is the failure path, and on a retrofit lock it is benign: when the batteries die, your key still opens the door, because the cylinder was never touched.
Keep that key somewhere other than inside the house it opens.
A tenant, or anybody trying the idea for the first time without committing to a cylinder change.
On sale from 130 € to 130 € on the German Amazon store at the time of checking.
Listed but with no offer on the British, French, Italian and Spanish Amazon stores — the reference exists there and nobody is currently selling it.
Not found on the American Amazon store, where the buy link falls back to a local search rather than to a page that does not exist.
Prices and availability are what Keepa reported on the date this page was updated; both move.
Prices quoted in this text were read on 2 September 2026. The live price is at the top of the page.
| Type | Retrofit — mounts over the existing lock |
|---|---|
| Access | Fingerprint, app, Bluetooth |
| Locking | Magnetic automatic locking |
| Power | 6 cells, stated by Signstek |
| Installation | No drilling; existing mechanism retained |
| Supplied | Indoor unit, outdoor keypad, mounting and app guides |
| Amazon reference | B0GKGHYBR2 (same reference on 5 Amazon marketplaces) |
| EAN | 6975795422471 |
No, and this is the most important sentence on the page. A retrofit lock turns the thumbturn you already have. The cylinder, the door and the frame are exactly as secure as they were before. What it changes is convenience and control over who can open it — not resistance to force.
Your key still works from outside, because the cylinder is unchanged. That is the structural advantage of retrofit locks over replacement ones: the fallback is the lock you already had. Keep a key somewhere that is not inside the locked house.
Retrofit locks need a thumbturn on the inside and enough clearance around it. Doors with a key-operated cylinder on both sides, or with a very short thumbturn, are the usual failures. Check the inside of your own door before ordering.
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 €
Retrofit · up to 18 unlock methods · full metal body, 50% slimmer · 9 months stated
SwitchBot states a next-generation motor, a full metal housing half as thick as its predecessor, up to eighteen unlocking methods with the Matter hub and touchscreen keypad, and a rechargeable main battery quoted at up to nine months.
Best for: A door where the indoor unit needs to be as unobtrusive as possible, on a household that likes options.
≈ 180 €
