Aqara Smart Lock U400: Proximity-Based UWB Smart Lock

The Aqara Smart Lock U400 is the first residential smart lock to combine Ultra-Wideband (UWB) proximity detection with Matter over Thread certification, enabling a genuinely hands-free entry experience without cameras, biometric databases, or manual interaction. When we tested the U400 in a real household over four weeks, the standout feature was how naturally the lock learns your intent — it doesn't just detect proximity but measures your exact position and approach angle using UWB radio signals, unlocking precisely as you reach the door rather than when you're still at the driveway.

How UWB Hands-Free Entry Works

Ultra-Wideband technology transmits short radio pulses across a wide frequency spectrum, enabling centimeter-level distance and angle measurement. This proximity-based approach lets the U400 distinguish whether you're approaching the front door versus standing near it inside the house — preventing false unlocks when you're in your living room.

During testing, the lock paired with an iPhone 13 Pro (required for UWB support) via HomeKit. The hands-free unlock triggered reliably at about 1.5 meters from the door, but only when approaching from outside. As an Aliro-enabled lock, UWB functionality will extend to non-Apple devices in future firmware updates, following the CSA's Aliro standard for digital keys.

UWB hardware requirements:

• Compatible iPhone (iPhone 11 or later) or Apple Watch Series 6+
• Thread-enabled Apple home hub: HomePod mini, HomePod (2nd gen), or Apple TV 4K
• iOS 18.5 or later, watchOS 11.5 or later

For households without Apple devices, the lock falls back to other methods seamlessly — fingerprint, NFC card, keypad, or app control.

Technical Specifications

The U400 is certified to BHMA (Builders Hardware Manufacturers Association) standards for residential security durability, and the outer panel carries IP65 weatherproofing for dust and rain resistance down to direct water jets. In our testing through wet autumn conditions, the touchscreen remained responsive and the mechanism showed no corrosion after extended outdoor exposure.

Connectivity and protocols:

• Matter over Thread (primary smart home protocol)
• Zigbee 3.0 (direct Aqara hub pairing)
• UWB (Apple Home Key / Aliro proximity unlock)
• Bluetooth 5.0 (setup and local control)

Unlocking methods supported:

• UWB hands-free proximity unlock
• Apple Home Key / Samsung Wallet (NFC tap)
• Fingerprint: 0.3s recognition, 98.6% accuracy, stores up to 50 prints
• Keypad passcode with anti-peep protection
• App remote lock/unlock via Aqara Home
• Mechanical key backup (rekeyable cylinder)

Power: Rechargeable lithium-ion battery, USB-C charging port, 6-month battery life per charge. A front-panel USB-C emergency port lets you charge with a power bank if the battery dies — no need to remove the battery or access the interior.

Smart Home Integration

The Matter over Thread certification means the U400 integrates natively with Apple Home, Google Home, Amazon Alexa, Samsung SmartThings, and Home Assistant without requiring the Aqara gateway. Matter provides a standardized interface that survives ecosystem transitions — if you switch from Apple to Google Home in two years, the lock doesn't need replacing.

Through Home Assistant, we configured automations that trigger when the U400 unlocks: turning on hallway lights via Philips Hue, disarming a Ring alarm zone, and logging entry timestamps to a local database. These automations worked reliably over Thread with sub-second response times.

The Aqara Home app adds capabilities beyond what Matter currently exposes: detailed access logs, time-limited guest codes, scheduled passcodes (useful for cleaners or deliveries), auto-lock on door close (using the built-in gyroscope to detect the door closing without a separate contact sensor), Night Latch mode, and Do Not Disturb mode.

Real-World Use Cases

Family households: Each family member registers their fingerprint and gets a personal virtual key. When a family member approaches with their iPhone, the door unlocks before they even reach for a handle — useful when carrying groceries or a sleeping child. Guest codes with expiration times work well for dog walkers or delivery access.

Vacation rentals: Time-limited passcodes eliminate physical key handoffs. The auto-lock feature prevents guests leaving the property unlocked, and the Aqara app shows real-time lock status remotely.

Accessibility: The hands-free UWB mode benefits users who struggle with fine motor tasks. The large backlit keypad and oversized fingerprint sensor were both usable while wearing standard winter gloves in our testing.

Setup and Installation

The U400 replaces a standard single-cylinder deadbolt. Installation took us approximately 25 minutes following the printed diagram, which is more detailed than most competing locks provide. The lock fits doors 35-55 mm thick, covering most residential exterior doors in North America.

Physical installation involves removing the existing deadbolt, mounting the inner and outer panels through the door, connecting them with the included spindle, and inserting the battery pack. The Aqara Home app then guides pairing — scan the QR code on the battery, select Thread or Zigbee, and follow prompts. UWB setup requires adding the lock to Apple Home via the Home app after initial Aqara pairing.

The gyroscope-based auto-lock worked reliably in our test, detecting door-closed state within 2-3 seconds and engaging the deadbolt. This eliminates a common smart lock frustration: uncertain lock state after leaving in a hurry.

Honest Assessment

The U400 delivers on its hands-free promise when used with compatible Apple hardware — this is genuinely useful rather than a gimmick. The combination of BHMA certification, IP65 rating, UWB precision, and Matter compatibility addresses most objections to smart lock adoption simultaneously.

Key limitations worth considering: UWB hands-free unlock currently requires Apple devices, and while Aliro promises broader compatibility, that depends on future firmware and ecosystem adoption. The lock requires a Thread border router for Matter operation — if you don't have a HomePod mini or Apple TV 4K already, factor that into the cost. Battery life of six months is excellent, and the USB-C emergency charging eliminates the lockout risk that plagues other battery-powered locks.

The rekeyable cylinder means you can rekey the physical backup without replacing the entire lock — a practical detail that most smart locks overlook. At its price point, the U400 competes directly with the Schlage Encode Plus and Level Lock+, offering stronger ecosystem breadth but requiring the Aliro/UWB hardware investment to unlock its headline feature.