August Lock 4th Gen: Retrofit Bluetooth Deadbolt with DoorSense

The August Lock 4th Gen is a Bluetooth retrofit deadbolt for renters and homeowners who want smart lock features without replacing exterior hardware. It fits over the interior thumb turn of your existing deadbolt. Your keys, cylinder, and exterior trim stay in place. This fourth-generation model keeps the core retrofit approach August is known for, at $149, it's the most affordable lock in the current August lineup.

This review covers the August Lock 4th Gen (model AUG-SL04-M01-G0X). It's worth knowing upfront: this model does not have built-in Wi-Fi. Remote access requires the separate August Connect bridge ($59). If you need remote control without an extra purchase, look at the August Wi-Fi Smart Lock Pro instead.

Hardware and Specs

The Lock 4th Gen mounts on the interior side of most standard American deadbolts. August ships a set of adapters for common thumb turn sizes. No drilling is required. Setup takes around 10 to 15 minutes with a standard screwdriver and the August app guide.

The lock runs on Bluetooth 4.0 for all phone communication. It uses 4 AA batteries, rated for about 6 months of normal use. The body is smaller and lighter than older August models. August also improved the motor noise on this generation - it's noticeably quieter than the third-gen model.

Key Specs

• Retrofit design: fits over existing deadbolt interior thumb turn
• Wireless: Bluetooth 4.0 (Bluetooth range only without bridge)
• Voice control: Alexa, Google, HomeKit (all require August Connect bridge, $59)
• DoorSense: door open/closed detection, included in the box
• Battery: 4x AA (approximately 6 months)
• Price: $149 USD

App Experience and Bluetooth Range

Without the Connect bridge, the August app works when your phone is within Bluetooth range, roughly 30 to 50 feet in a typical home. You can lock, unlock, check status, and view the access log. Guest keys work over Bluetooth too - send a virtual key to a guest's phone and they can use it within range.

Auto-lock runs on a timer you set in the app, from 30 seconds to 30 minutes. DoorSense keeps it honest: the lock checks whether the door is fully closed before throwing the bolt. This is a practical detail that prevents the deadbolt from jamming against an open door.

Auto-unlock uses your phone's location. As you approach home, the app watches for your Bluetooth signal and unlocks when you're at the door. It's a two-step detection to reduce false unlocks from passing nearby.

The app is clean and responsive. Access history shows every lock and unlock event with a timestamp and who triggered it. You can create guest keys with expiration dates, useful for short-term visitors or service appointments.

Smart Home Works With Connect Bridge

This is the part that trips up buyers. Smart home voice control on this lock requires the August Connect bridge. The bridge plugs into a wall outlet near the door and adds Wi-Fi, which lets the lock reach Alexa, Google Assistant, and Apple HomeKit.

With the bridge installed, you get:

• Remote lock and unlock from anywhere
• Alexa and Google voice commands
• Apple HomeKit and Siri support
• Real-time alerts and push notifications

Without it, you get Bluetooth-only app control. That's still useful at home, but it's a meaningful limitation if you travel or want voice assistant routines. The $59 bridge cost brings the total to $208, which starts overlapping with the Wi-Fi Smart Lock Pro price range.

For Home Assistant users, the August Connect bridge also enables Home Assistant cloud integration. Local-only Home Assistant control isn't supported without the bridge.

Who Should Buy This Lock

The August Lock 4th Gen is a solid pick for a specific type of buyer: someone who mostly needs smart lock features at home and doesn't care about remote access from outside. Renters who can't modify exterior hardware benefit from the retrofit design. It keeps your existing keys working and leaves no trace when you remove it.

It's also a reasonable entry point if you're testing smart locks before committing to a full ecosystem. The Bluetooth-only experience is reliable and the auto-lock with DoorSense works well day to day. You can always add the Connect bridge later if you decide you want remote access.

Who should look elsewhere: if you want remote access from the start, the August Wi-Fi Smart Lock Pro has built-in Wi-Fi and no bridge needed. If you want a keypad for entry without a phone, look at the Schlage Encode Plus or Yale Assure 2. The August Lock 4th Gen has no keypad option.

Final Thoughts

At $149 with Bluetooth and DoorSense included, the August Lock 4th Gen delivers what it promises. It's not the most full-featured smart lock, but it's a clean, reliable retrofit for home Bluetooth use. The motor is quieter than prior generations. Setup is straightforward. The app works well. DoorSense adds genuine practical value to auto-lock.

The bridge requirement for remote access and voice control is the main trade-off. Budget $208 total if you want the full feature set. At that price point, compare it against the Wi-Fi Smart Lock Pro before buying.

For official specs and current pricing, see the August Lock 4th Gen product page.