The question always comes up at the same point in the visit, just as we start talking about taking keys out of the equation: “but can't someone hack it?” Behind it is the image of someone opening your door from a laptop, remotely, without touching a thing. It's a reasonable worry — and it's aimed at the wrong target.

The honest answer is that a smart lock changes how your door opens, not what holds it shut. Almost everything that determines how hard your home is to break into stays exactly as it was before the lock went on. What it does bring are three new, legitimate concerns: the battery, getting locked out and the digital side. Let's take all three, one by one, along with what you should insist on before you let anyone fit one for you.

Fear 1: “What if the battery dies just as I get home?”

It's the objection we hear most, and the one that least survives contact with reality. These locks run on ordinary batteries that last in the region of a year, and they don't cut out all of a sudden: they warn you weeks in advance, in the app and on the door itself, once the charge starts to drop. To actually end up stranded, you'd have to ignore the warning for many days running.

And even if you do ignore it, you're not locked out: on models that fit over your existing cylinder, your usual keys still open the door. The physical key doesn't disappear; it becomes the plan B you carry in your pocket or leave at work. Models with a keypad also give you a code, which depends on neither your phone nor the connection. The rule we always apply is the same: never just one way of opening the door.

Fear 2: “What if I get locked out?”

It's worth turning this fear on its head. With a conventional lock you have one way into your home: the key. If you lose it or leave it inside, you're stuck outside and it's time to call a locksmith. With a properly fitted smart lock you have four — key, code, fingerprint and phone — and all of them would have to fail at once for you to have a problem.

The specific worry people raise, “my phone's battery has died”, isn't what it seems either: opening from your phone works by proximity, talking directly to the lock, not by travelling to a server and back. If there's no internet at home, the door opens just the same. What you lose without a connection are the extras — opening remotely to let someone in, or checking the access log from the office — not the essential part, which is getting into your home when you're standing right in front of it.

Fear 3: “Can someone open my door over the internet?”

This one does call for a serious conversation, and the answer depends entirely on an architectural decision that almost nobody explains when they sell you the lock: where your digital keys live.

In the most common setup, the lock is tied to a cloud account with the manufacturer. Your opening credentials sit on a server that isn't yours, and the attack surface stops being your door and becomes that company's database. Nobody needs to force anything on your landing: a data breach a thousand kilometres away is enough. It's also why, if that manufacturer shuts down the service or has an outage, whole features of your lock simply switch off and there's nothing you can do about it.

The alternative is to manage it from a system on your own local network, with no cloud account in between. Digital keys, codes and the access log stay inside your home, with bank-grade encryption on the link to the lock, and there's no outside server for them to leak from. It's the same logic we apply to cameras, and it's why we set up access control and smart locks this way: not because the cloud is the devil, but because it makes no sense to keep the keys to your home somewhere you don't control.

Whatever the system, the basic precautions that INCIBE, Spain's national cybersecurity institute, recommends for any connected device (in Spanish) apply here too: change the factory-default passwords, keep the firmware up to date and don't hang the system off a poorly secured Wi-Fi network. An installer who doesn't bring any of this up is a warning sign in its own right.

What really decides how secure your door is: the cylinder

And now for the part that rarely makes it into the adverts. A smart lock fitted over your cylinder inherits that cylinder's security. If the cylinder that's been in your door for twenty years gives way to a mechanical opening technique, it will give way in exactly the same way once the electronics are fitted: doors don't get opened through the smart side, they get opened through the dumb one.

This isn't an argument against smart locks — they don't make anything worse — but it does change where your money is best spent. If you're going to invest in your door, the sensible thing is to do both at once: a decent security cylinder with anti-bump and anti-drill protection, and the smart layer on top. The cylinder is the cheap part of the quote, and it's the part that holds everything else up. When someone asks us for just the electronics and their cylinder is on its last legs, we tell them so before we install anything.

Types of smart lock, and what each one involves

Over your existing cylinder

It's the most common type and the one we install by default. The motor mounts on the inside face of the door, over the cylinder you already have: from the outside your door looks identical, your keys keep working and the whole installation can be undone in an afternoon. Because it touches neither the door leaf nor the wall, it's done with no building work of any kind, which makes it the realistic option if you rent: it comes off and goes with you to your next home.

Replacing the cylinder or the lock

If the cylinder is worn or low-security, or the door has a multipoint lock operated with a handle, the sensible thing is to replace it with one designed for motorisation. You gain in robustness and integration, and it's the perfect opportunity to upgrade the cylinder. The trade-off is that it's no longer a fit you can undo in five minutes, so if you rent you'll need to talk it over with your landlord. If you're not sure which of the two cases applies to your door, here's how to check it yourself in five minutes.

What you can add to it

A keypad for codes, a fingerprint reader and, above all, a connected video door entry system: see who's calling and talk to them from wherever you are, with every call logged with a photo and the time. It's the combination that turns the lock into more than a convenience — you go from “I get in without keys” to “I know what's going on at my door”.

Checklist: what to insist on before you install one

  • A physical backup key that still opens the door whatever happens to the electronics.
  • Battery warnings weeks in advance, not a red light on the day it dies.
  • Opening without internet: when you're standing at the door, you shouldn't need a connection.
  • Knowing where your credentials are stored: on your local system or on a manufacturer's server. Ask the question outright.
  • An access log you can check, so you know who came in and when.
  • Being able to revoke a code or a digital key yourself in seconds, without calling anyone.
  • Factory passwords changed and updatable firmware, with who takes care of it set down in writing.
  • A cylinder that lives up to what you're protecting.

When it's really worth it

If all you're after is not having to take the key out of your pocket, it's probably not worth the outlay. What justifies a smart lock is managing access, and you notice it the day you stop handing out copies: you create a code with set hours for your cleaner, for builders or for whoever comes round to water the plants, and that code expires on its own. No more changing the cylinder because a key is floating around somewhere, and no more hiding a spare under the doormat when a family member is arriving and nobody's home.

It's also the piece you miss when the house is left empty: you can let a neighbour in on a one-off basis without leaving them your keys for a fortnight, see in the log that they did go in on Tuesday, and withdraw their access as soon as you're back. And because everything runs on the same system, the house responds when the door opens — the hall light, the climate control, the alarm disarming itself — instead of being just one more standalone gadget.

Common questions

Is a smart lock easier to force open than a regular one?

No, because the part that stands up to a physical attack doesn't change. A model that fits over your existing cylinder leaves that cylinder and the door's anchoring points untouched: from the outside, a burglar finds exactly the same lock as before. The electronics sit on the inside face, where nobody can tamper with them without already being inside. What does change is that you now know when the door was opened and who opened it.

Does it still work if there's a power cut at home?

Yes. The lock doesn't run off the mains but on its own batteries, so a power cut doesn't affect it: it opens just the same with the key, a code or your phone at the door. The only thing a power cut knocks out is the router, and with it remote checking from outside the house — not opening the door, which is handled right at the door itself.

Can the manufacturer or the installer open my door?

It depends on where the credentials live. If the lock works through a cloud account with the manufacturer, that company by definition has the technical ability to manage access to your home. If it's administered from your local system, the digital keys are in your home and only you control them. For our part, once an installation is finished, you are the system administrator: we don't keep open access to any client's home.

What happens if my phone is stolen?

You revoke that digital key from any other device and it stops opening the door instantly — something you can't do with a lost physical key without changing the cylinder. It's also worth having the app ask for a fingerprint or PIN before it opens, so that an unlocked phone in someone else's hands still isn't a key. And the access log will tell you if anyone tried to use it.

What if my door is old or has a three-point lock?

In most cases it can be done, but that's exactly what needs checking during the visit: the type of cylinder, how far it sticks out on the inside, and whether the lock is single-point or multipoint. Three-point locks operated with a handle usually need a different motorised model from a simple door. It's a five-minute check that saves you from buying a device that then doesn't fit.

In short

Are smart locks safe? Yes, on two conditions that depend on how they're installed rather than on the device: there must never be just one way of opening the door, and your digital keys must live in your home, not in a company's account. With that in place, a smart lock doesn't weaken your door — it leaves it just as strong on the outside and a good deal smarter on the inside. And if you really want it to be more secure than it was yesterday, start with the cylinder: it's the boring, cheap part, and the one that holds everything else up.