Aqara U400 review: HomeKit’s futuristic smart lock has arrived

I bought my first house earlier this year, so being the nerd that I am, I’ve prioritized turning my house into a smart home. First on the list was a smart lock.

I knew I wanted something with the best possible HomeKit integration, and the Aqara UWB Smart Lock U400 seemed to fit that bill on paper. So far, I’ve been highly impressed thanks to Ultra Wideband support.

Installation

Installation of the Aqara U400 was pretty straightforward, following this video from Aqara’s YouTube channel. It’s more involved than installing the August smart locks I’ve used in the past, but for good reason. Whereas the August locks typically fit over your existing deadbolt, the Aqara lock replaces the entire system.

So in exchange for that slightly trickier installation process, you get a more reliable and “integrated” experience.

I installed two Aqara U400 locks, one at the back door and one at the front door. Going into the process, I was a bit worried about the front door installation. It’s an older door, and the previous deadbolt tended to get stuck if it wasn’t perfectly aligned with the striker plate.

Surprisingly, this was not an issue with the Aqara lock. Again, this is a benefit of how the Aqara lock replaces the deadbolt itself, rather than being a retrofit solution. I’ve also found that the Aqara lock is less sensitive to resistance from the striker plate. Whereas the August lock would get “jammed” with even the slightest bit of resistance, the Aqara lock has enough force to power through even if it does get slightly stuck.

All in all, it took about an hour to install both Aqara smart locks. The trickiest part was actually connecting the two tiny wires to the back of the lock itself. The wires are super fragile, so proceed with caution there.

Using the Aqara UWB Smart Lock U400

What makes the Aqara U400 stand out is just how many ways there are to unlock it.

First, the Aqara U400 supports NFC for “tap to unlock.” Most notably, this also works with Express Mode on your iPhone and Apple Watch. This means you can simply tap your iPhone or Apple Watch to lock or unlock your door, without opening the Wallet app or authenticating with Face ID or Touch ID.

But here’s where things get really fun: support for UWB, or Ultra Wideband connectivity. Apple added support for UWB to HomeKit in iOS 18, and the Aqara U400 is the first to take advantage of it.

UWB lets devices understand exactly where they are relative to each other. Compared to Bluetooth, which is more about general proximity, UWB enables much more precise, spatial awareness, so devices can react based on your exact position and movement. It’s the same technology that powers the communication between your iPhone and AirTag, for example.

For the Aqara U400, this means that when I approach my door with my iPhone in my pocket or my Apple Watch on my wrist, my door unlocks before my hand even reaches the handle. I don’t have to wait a few seconds when I approach the door.

To me, this is the pinnacle of the smart lock experience. It’s the experience we’ve been promised for years, made possible by UWB technology. It’s probably the most “it just works” experience I’ve ever had with HomeKit.

In the Home app, you can even control the “Approach Direction” for the Aqara U400’s UWB support. You can choose whether the door unlocks when you approach from the left, front, or right — or all of the above.

In addition to NFC and UWB, you can manually unlock the Aqara U400 in the Home app or the Aqara app. The Home app integration is lightning fast, by the way. Much faster than any previous smart lock I’ve used.

You can also enter a passcode on the lock’s touchpad (which you can set in HomeKit) or use your fingerprint (which you can set up in the Aqara app). There’s a bit of bouncing back and forth between apps required to enable all of these options, but most can be done in the Home app.

Finally, there’s a hidden physical key, so you can lock or unlock your door the old-fashioned way if needed. You can also rig up various automations in the Home app, as usual.

And when it comes time to lock the Aqara U400, you can do so from the outside by tapping your iPhone or Apple Watch on the lock or by tapping the lock button on the touchpad. You can also enable auto-lock in the Home app or the Aqara app, which will lock it after X minutes.

Unlike the August locks I’ve used in the past, the Aqara U400 uses a rechargeable USB-C battery. Aqara says the battery “lasts up to 6 months per charge.” I haven’t had the lock long enough to test that. You can use the lock’s USB-C port to recharge it, or you can pop the battery out and plug it in separately. I’m happy to ditch the awkward CR123A batteries my August lock used.

Wrap up

I’ve used HomeKit smart locks for years, but the Aqara U400 is the first one that truly delivers on the smart home vision we were promised from the start. With previous smart locks, there were always a few compromises I had to make and multiple asterisks that came with using them. That’s not the case with the Aqara U400. It’s very “set it and forget it.”

As it stands right now, the Aqara U400 is the only smart lock that supports UWB in Apple Home. Hopefully, that changes sooner rather than later. For now, however, credit to Aqara for being first and nailing the implementation.

You can order the Aqara UWB Smart Lock U400 on Amazon. It’s pricey at $269.99, but well worth it for the convenience in my opinion.

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