Aqara Smart Lock U400, w/ Matter over Thread, HomeKey, Ultra Wideband (review)

I’ve lost count of how many smart locks I’ve tested so far, but a fair number of them have come from Aqara, namely the A100 Zigbee, U100, U50, and U200. I was also sent the U300, although that particular unit turned out to be faulty. Now, however, I’m finally in a position to review the U400, which I’ve had installed for around a couple of months. I can safely say it’s not only the best Aqara lock I’ve tested to date, but probably the best smart lock from any company I’ve reviewed so far.

The A100 Zigbee is still serving me well and remains one of my favourites, but it lacks the one feature that really sets the U400 apart, Ultra Wideband support. So what exactly is that? In simple terms, it allows the UWB radio in the lock to detect the UWB radio in your iPhone, series 11 and later, excluding the budget models, and unlock automatically as you approach. Crucially, it does this with a level of precision that Bluetooth simply can’t match.

Many smart locks have offered some form of auto-unlock for years using Bluetooth, but UWB is faster, far more accurate, and considerably smarter. It can determine which side of the door you’re on, so it won’t unlock if you approach from inside, for example. It also doesn’t rely on you leaving a minimum geographical area before it knows how to react, which is a common limitation with Bluetooth-based solutions. It all sounds very promising, so read on to see how it performs in practice, along with what else makes this a compelling option for anyone using a deadbolt.

PACKAGING | CONTENTS

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The packaging for the U400 shows the lock prominently on the front, very much in the Apple style, and proudly lists a wide range of supported platforms and standards, including Matter, Apple Home, Amazon Alexa, Samsung SmartThings, Google Home, and even Home Assistant. Thread is also mentioned prominently here of course.

There’s also a BHMA Certified logo on the top of the box, although it’s worth noting that this only meets the basic level 3 requirement.

One side of the packaging lists the core specifications, including the wireless protocols in use, Thread, Bluetooth, NFC, and UWB. It also notes an IP65 rating, although this only applies to the external assembly, which is entirely expected.

The other side highlights a selection of headline features:

• Hands-free unlock with Apple HomeKey
• Matter over Thread
• Rechargeable battery
• IP65 and BHMA certified
• Advanced fingerprint reader
• Auto-lock assurance

The last two are somewhat vague. It’s not immediately clear what makes the fingerprint reader more advanced than those found on the U50, U100, U200, or even the U300. “Auto-lock assurance” is equally ambiguous, although it appears to be little more than a reassuring way of saying the lock supports auto-locking.

Along the bottom of the box is the usual legal text, but buried within it is an important detail. Because the U400 uses Matter over Thread, you’ll need both a Matter controller and a Thread Border Router to get meaningful functionality from the lock.

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Inside the box you’ll find the inner and outer assemblies, along with a template to help cut the correct holes if you’re fitting it to a fresh door. There’s a manual, which is adequate for the basics but not especially detailed, and two traditional keys. You also get a separate box containing the deadbolt and associated parts, a bag of screws, and finally the rechargeable battery itself.

I don’t mind the move to a rechargeable battery, although Aqara has been oddly quiet about whether spare batteries will be available to purchase, which does make me a little uneasy.

THE U400

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Design-wise, the U400 isn’t a radical departure from the U100, but it has clearly been refined. The corners are much more rounded, and the keypad digits are now almost invisible, giving the lock the appearance of a dark slab. Personally, that suits my tastes perfectly. Overall, it looks more mature and more considered.

The battery compartment is also thankfully far easier to access than on the U50 and U100. That might not sound like a big deal, but it absolutely is to me. I don’t enjoy wrestling with something that should take seconds to deal with.

The battery itself can be charged in a few different ways. If you want to keep the lock active while it’s charging, you can use the USB-C port on the underside of the inner assembly. Alternatively, you can charge the battery directly using the USB-C port on the battery itself, although if you do it this way, the battery won’t show as charging in either app. When charging via the inner assembly, it does report its charging status correctly.

Overall, the lock feels like a definite step up from earlier Aqara models, even if some of the materials used remain broadly the same.

Even though this is a Matter over Thread lock, you can still add it to Aqara Home without using a Matter controller or a Thread Border Router. This is something I also did with my U200, but in that scenario, control is limited to a direct Bluetooth connection.

Adding the U400 to Aqara Home doesn’t require either the Aqara QR code or the Matter QR code. Even when Matter is in use, the lock is added and configured without directly involving Matter within the Aqara app itself. This means you can add the lock to Aqara first, then add it to Apple Home either from within the Aqara app or directly in Apple Home using the single Matter QR code. Once that code has been used, however, any additional ecosystems you want to add will require a new code.

INSTALLATION – APPLE HOME

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One nice touch on the physical installation side, which I won’t go into too much detail on here, is the inclusion of a removable adaptor or collar. This is designed for doors with smaller bore holes than the standard deadbolt size. Leave it in place and it slots neatly into standard holes, remove it and the lock can be fitted to doors with smaller openings.

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Assuming you’ve got at least one Apple Home hub that also acts as a Thread Border Router, you can add the U400 directly to Apple Home. Traditionally, tasks like adding fingerprints would require the Aqara app, but Aqara has taken a bold step here by allowing fingerprints to be added directly via a specific sequence of taps on the keypad, without opening the Aqara app at all.

That said, I still think it’s sensible to add the U400 to Aqara Home, as some settings may still require it. For now, though, I’ll focus on how the lock behaves within Apple Home.

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As expected, you’re presented with a single tile representing the lock, along with a simple toggle to lock or unlock it.

Inside the settings page, you’ll find the usual battery level and charging status. There’s also a new option I’ve not seen on smart locks before, called Approach Direction. This is directly tied to the Ultra Wideband functionality and allows the lock to understand which direction you’re likely to approach from when you’re outside.

For most people in houses, this will be straight on from the front. However, for those with side entrances, or apartment dwellers who might approach their door from the left or right along a corridor, these options allow the U400 to respond more intelligently.

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There’s also the Manage Access section, which lets you grant access to people who aren’t members of your Apple Home setup. This can be done via a passcode or by issuing them their own Apple HomeKey, even without adding them to your home.

Auto-lock can be enabled and configured here too, with options ranging from disabled, through 30 seconds, all the way up to 30 minutes.

Finally, Connected Services shows which ecosystems the lock is currently linked to. In my case, it’s connected to both Apple Home and Aqara.

IN AQARA HOME

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I’ve said this many times before, but the Aqara app generally exposes more functionality for Aqara devices than other ecosystems, and the U400 is no exception.

The main screen displays a good amount of information, starting with the state of both the lock and the door. You can clearly see whether the door itself is open or closed, as well as whether the lock is currently locked or unlocked.

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Bluetooth is used for direct connections when adjusting certain settings, and the app also shows that my U400 is connected to an Aqara Matter controller.

User management is something I’ve covered extensively with previous Aqara locks, so I won’t go into too much depth here. You can create one-time passwords, add users on a temporary or permanent basis, and fine-tune access in ways that go beyond what’s currently available via Manage Access in Apple Home. That said, Apple HomeKey itself lives exclusively within Apple Home, not the Aqara app.

You can, of course, lock and unlock the door from this screen using the button at the bottom, whether you’re on the local network or accessing it remotely. The settings panel offers even more granular control.

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The Voice & Sound section lets you adjust the audio feedback from the lock, including alarms.

There’s also an option to link devices, which currently includes the E1 and G5 Pro cameras, as well as the G410 video doorbell. This allows live video feeds to appear alongside the U400 within the app. If, for example, you have a G410 or G4 doorbell on the same door as the U400, you can see who’s there and unlock the door from a single screen.

Auto-lock settings in the Aqara app are independent of those in Apple Home, so it’s best to configure one or the other, not both. The Aqara app allows a maximum delay of 10 minutes compared to 30 minutes in Apple Home, but it also offers immediate locking, which Apple Home doesn’t. The minimum delay is 3 seconds in Aqara, versus 30 seconds in Apple Home.

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Do Not Disturb mode is useful if you want to minimise late-night sounds from the lock. Beyond that, there are additional options for Matter settings, firmware updates, and automations. Automation options aren’t especially extensive, but you can use the lock state as a trigger. These include conditions such as Not Fully Locked, which likely indicates the door is open or possibly jammed, as well as Low Battery Detected and Battery Charged.

IN PRACTICAL USE

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At the moment, the U400 is fitted to an internal door, as our main entrance is still using the Aqara A100 Zigbee. We’ll be moving to a new place at some point soon, though, so there’s a good chance I’ll be able to install it on a proper front door in the future.

As it stands, this is one of those devices that’s far better appreciated in action than described in text, so I’d strongly recommend checking out the video. What I can say here is that UWB is a completely different experience compared to Bluetooth.

My only real experience with Bluetooth auto-unlock comes from a second-generation Nuki lock we previously used. Because we live in an apartment where there’s very little distance between the lift and our door, Bluetooth rarely had time to connect before I was already standing in front of it.

Bluetooth auto-unlock works by estimating proximity based on signal strength. Your phone advertises itself using Bluetooth Low Energy, the lock detects that signal, and then measures RSSI, or Received Signal Strength Indicator. If the signal appears strong enough, the system assumes the phone is nearby and triggers an unlock. The problem is that signal strength fluctuates due to walls, reflections, body absorption, and interference. To compensate, the lock has to average readings and apply thresholds, which makes the process imprecise and sometimes slow, as it waits for the signal to stabilise.

Ultra-Wideband works very differently. My iPhone 15 Pro Max and the lock exchange extremely short radio pulses and measure the precise time it takes for those signals to travel between them. Because radio waves move at the speed of light, this timing directly translates into distance with centimetre-level accuracy. The U400 can also determine direction, meaning it knows not just that your phone is close, but that it’s directly in front of the door and approaching it.

UWB is generally faster because it doesn’t have to guess or smooth out noisy signal strength data. It performs a precise distance measurement almost instantly and can apply a clear rule, such as unlocking when the phone is within half a metre and moving towards the door. Bluetooth, by contrast, relies on fluctuating signal estimates and therefore needs filtering and safety delays. In short, Bluetooth infers proximity, while UWB measures actual physical distance.

In terms of reaction times, the U400 is excellent. Very occasionally there might be a slight delay, but it’s still nothing like Bluetooth-based solutions. Even if something does go wrong, you’ve still got plenty of fallback options, including HomeKey, the fingerprint reader, the keypad, NFC, traditional keys, or simply unlocking via Apple Home or Aqara Home.

SUMMING UP

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I’ll make no bones about it, I really like this lock. A lot of that comes down to the UWB feature, but even without it, the U400 is at least as good as the U100, with a noticeably improved design.

HomeKey remains a great feature, but for some people the fingerprint reader had already relegated it to an afterthought. Now, with UWB, which effectively acts as an extension of HomeKey within Apple Home, we’ve got yet another reason for HomeKey to take a back seat, unless you’re using an iPhone without UWB, of course.

Matter over Thread hasn’t featured heavily in this review, but it’s worth noting that this is Aqara’s first deadbolt lock to offer Matter over Thread. The U200 also supports Matter over Thread, but it’s a retrofit design that works with both deadbolt and mortice locks. The U50 and U100 still rely on Bluetooth for Apple Home, although using them via an Aqara hub brings Zigbee into play, which is a bit faster. With Matter over Thread, you’re getting a degree of future-proofing alongside improved responsiveness, which is nothing to be sniffed at.

There’s an inevitable price increase for this new level of convenience, but if cost isn’t your primary concern and you’re currently considering the U50 or U100, stop and get the U400 instead. You won’t regret it.