The Aqara Smart Lock U400 is an interesting choice if you want a digital door lock that offers more than the usual fingerprint and password options. The feature that stands out most is its Ultra-Wideband (UWB) unlocking. With an authorized iPhone or Apple Watch, the lock can unlock as you approach, so you do not need to enter a code or touch the fingerprint reader.

That hands-free approach could be especially useful when your hands are full, you are carrying groceries, dealing with heavy rain, or wearing gloves. Instead of stopping to find a key or operate the lock, the U400 is designed to recognize your approach and unlock when you are ready to enter.

What makes the Aqara Smart Lock U400 more practical is that UWB is not the only option. It also supports Apple Home Key, Samsung Wallet Digital Home Key, fingerprint unlocking, permanent passwords, offline passwords, scheduled passwords, NFC cards, app control, voice control and a mechanical key. So users have several ways to access the door depending on their preferences.

UWB Hands-Free Unlocking

UWB is easily the most distinctive feature of this smart door lock. The U400 uses range and angle measurements to identify your position and understand your unlock intention. The idea is that it unlocks when you are actually ready to enter rather than simply unlocking because an authorized device happens to be nearby.

For everyday use, I can see the appeal. Carrying bags is one situation where hands-free access makes sense. Heavy rain is another, since you do not have to search for keys or operate a touchscreen. Gloves can also make keys, keypads and fingerprint readers less convenient, so being able to approach the door is a useful alternative.

There is an important compatibility requirement, though. UWB unlocking works with select iPhone and Apple Watch models and requires a Thread-enabled Apple home hub, such as a HomePod mini or Apple TV 4K. I would check compatibility before purchasing rather than assuming every Apple device supports it.

Multiple Ways to Unlock

One thing I particularly like about the U400 is that you are not dependent on one access method.

Apple users can add Home Key to Apple Wallet and unlock with an iPhone or Apple Watch. The supplied information states that the Home Key can work even when the devices are powered off. It can also be shared with family members, while guest codes can be provided to visitors.

Samsung users can use Digital Home Key through Samsung Wallet when the lock is connected to Samsung SmartThings. This also supports unlocking when the phone is powered off, and household members can be invited to use the Home Key.

The fingerprint reader provides another convenient option. It can store up to 50 fingerprints and is rated for unlocking in 0.3 seconds, with a stated recognition rate of up to 98.6%.

There are also permanent, offline and scheduled passwords, NFC card access and a mechanical key. Having these choices is useful because different people may prefer different methods. One person might use a fingerprint, while another may prefer a smartphone or physical key.

Smart-Home Integration

The U400 is not just a standalone digital lock. It supports Matter over Thread and works with Aqara Home, Apple Home, Google Home, Amazon Alexa, Samsung SmartThings and Home Assistant.

For people already using smart-home devices, this is a useful advantage. The U400 can also be connected with other Aqara products to create personalized smart-home scenarios.

Another feature worth mentioning is its integration with the Aqara Doorbell Camera Hub G410. According to the supplied information, the combination allows you to see who is at the door and unlock directly through the Apple Home app.

The U400 also supports app control and voice control. However, the information provided does not list every function available through these options, so I would check the exact capabilities before buying if a particular app or voice function is important to you.

Auto-Locking and Weather Resistance

The built-in gyro sensor detects when the door is closed and can automatically lock it. No additional contact sensor is required.

This is a simple feature, but it could make everyday use easier. There is no need to remember to manually lock the door after closing it.

The outer panel has an IP65 weatherproof rating and is designed to withstand dust, splashes and heavy rain. That is useful if the exterior part of the lock is exposed to outdoor conditions.

The U400 also has a rekeyable design. The physical key can be changed without replacing the entire lock cylinder, which is a useful option for people who still want conventional key access.

Battery and Charging

The U400 uses rechargeable batteries and is stated to provide up to six months of use on a single charge. A full charge takes a few hours.

Charging is handled through a built-in USB-C port. The lock can be charged using a power bank without removing the battery or cover, which is convenient.

There is also a low-battery notification when the battery reaches 20%, giving you a reminder to recharge. If the battery runs low, the emergency USB-C charging port allows power from a power bank or a phone that supports USB-C to USB-C power supply.

The six-month figure is an “up to” claim, so I would treat it as the stated maximum rather than expecting exactly six months regardless of usage.

Security Features

The U400 combines several access methods, including fingerprints, passwords, digital home keys, NFC and a mechanical key. It is also described as BHMA certified and as meeting an industry standard for reliable residential security and durability.

The IP65 rating is another practical feature for weather exposure.

That said, I would separate convenience from security. Features such as UWB and automatic locking make the lock easier to use, but the supplied information does not justify claiming that it guarantees protection against burglary or hacking.

Things to Check Before Buying

The biggest consideration is compatibility. The U400 supports several smart-home ecosystems, but individual features can have specific requirements. UWB, in particular, requires compatible Apple devices and a Thread-enabled Apple home hub.

I would also verify installation compatibility before purchasing. The information provided does not specify door dimensions, door types or installation requirements, so it is important to confirm that the lock is suitable for the intended door.

It is also worth considering whether you will use all the smart features. If you only want fingerprint access and a mechanical key, the extensive smart-home functionality may be unnecessary. But if you already use Apple Home, Samsung SmartThings, Google Home or another supported platform, the additional integration could be much more useful.

Final Verdict

When compared with other Aqara Digital Lock, Aqara U400 is a flexible smart door lock with UWB hands-free unlocking as its main highlight. Being able to approach with an authorized iPhone or Apple Watch and unlock without touching the lock could be genuinely convenient when your hands are full, it is raining or you are wearing gloves.

At the same time, you are not limited to UWB. Apple Home Key, Samsung Wallet Digital Home Key, fingerprint access, multiple password options, NFC, app and voice control, and a mechanical key provide plenty of alternatives.

The rechargeable USB-C battery, low-battery warning, emergency charging, automatic locking, IP65 weather resistance and Matter over Thread support add to its practical appeal.

I would mainly consider the U400 for someone who will actually use its smart features and wants multiple ways to manage access. Before buying, I would confirm device compatibility and make sure the lock is suitable for the specific door. If those requirements are met, the Aqara Smart Lock U400 offers a convenient and versatile approach to everyday home access without forcing everyone to use the same unlocking method.

Want to compare it with other models? Check out our digital lock reviews to explore more smart locks, their features, pros and cons, and see which option may be the right fit for your home.