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 conclusion The cheap way in, and the honest way to describe it is convenience rather than security. For a tenant it is one of the retrofit locks in this hub, which fit without drilling — unlike the replacement deadbolts and handle sets.
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 inside key left in the existing cylinder, or its thumbturn where there is one. 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 neighboring 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. Signstek recommends an emergency-function or thumbturn cylinder: with one, when the batteries die, your key still opens the door from outside, because the cylinder was never changed. With an ordinary cylinder and a key left on the inside, that fallback does not exist.
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.
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.
| Type | Retrofit — mounts over the existing lock |
|---|---|
| Access | Fingerprint, code on a backlit keypad, app, Bluetooth, mechanical key; temporary codes for guests |
| Locking | Magnetic automatic locking |
| Power | 6 AA batteries, not supplied |
| Installation | No drilling; existing mechanism retained |
| Supplied | Indoor unit, outdoor keypad, mounting and app guides |
| Compatibility | Inside key up to 7 mm (0.28 in) thick and 39 mm (1.54 in) protrusion; cylinder adapters supplied; emergency-function cylinder recommended |
| Fingerprint data | Stored locally on the lock, stated by Signstek |
| Amazon reference | B0GKGHYBR2 |
| EAN | 6975795422471 |
No, and this is the most important sentence on the page. A retrofit lock turns the inside key left in the existing cylinder, or its thumbturn where there is one. 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.
With an emergency-function or thumbturn cylinder, which Signstek recommends, your key still opens it from outside, because the cylinder is unchanged. With an ordinary cylinder that has a key left in it on the inside, the outside key cannot go in: check your cylinder before relying on this fallback. 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.
This one also fits over a key left on the inside, if that key is no more than 7 mm (0.28 in) thick and protrudes no more than 39 mm (1.54 in) from the cylinder; cylinder adapters are supplied. Check the inside of your own door before ordering.
7.2/ 10
The cheap way in, and the honest way to describe it is convenience rather than security. For a tenant it is one of the retrofit locks in this hub, which fit without drilling — unlike the replacement deadbolts and handle sets.
A reference exists on these Amazon stores: France, Germany, Italy, Spain, United Kingdom. Listed is not the same as in stock — availability changes daily.
Details checked on September 2, 2026.
A first smart lock, and particularly a rented apartment where nothing may be altered.
Specifications: the manufacturer sheet for home security products and the matching Amazon product page. Prices and availability: Keepa. Every figure on this page names its source.
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.
Retrofit · built-in Wi-Fi, no bridge · Matter over Thread · 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.
APPLE HOME native, no hub required, plus Google Home, Alexa and SmartThings · up to 8 months on 8 AA — AND THE ONLY LOCK HERE THAT PUBLISHES THE ASSUMPTION: approximately 10 unlocks per day · app, keypad, physical key or voice · 18 months electronic and 36 months mechanical cover, the only split warranty on this shelf · no fingerprint reader · a key and no emergency terminal
The only battery figure on this shelf with its assumption printed next to it — eight months at about ten unlocks a day.
Best for: An Apple household that wants the lock in the Home app without a bridge
≈ $80
