August Lock 4th Gen: Retrofit Bluetooth Deadbolt with DoorSense

At $149, the August Lock 4th Gen (model AUG-SL04-M01-G0X) is the cheapest lock August currently sells, and that price buys a Bluetooth-only retrofit that clips over the interior thumb turn of your existing deadbolt. Your keys, cylinder, and exterior trim never change. That makes it an easy yes for renters who can't touch the door hardware. The right August for you comes down to one question: do you ever need to lock the door when you're not home?

Here's what trips people up, and it shapes this whole review. This model has no built-in Wi-Fi. Remote access means buying the separate August Connect bridge ($59) on top. Need remote control out of the box? The August Wi-Fi Smart Lock Pro is the better starting point.

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.

Is the Lock 4th Gen Worth It?

Here's the short version. If your lock lives on a door you're usually home for, the Lock 4th Gen at $149 does the job without fuss. The motor is quieter than the 3rd Gen, DoorSense keeps auto-lock from jamming against an open door, and the app rarely fumbles a Bluetooth 4.0 command.

The catch is the same one August has shipped for years. No built-in Wi-Fi. Want voice control or remote locking, and you're buying the $59 bridge, which drags the real total to $208. That's uncomfortably close to Wi-Fi Smart Lock Pro money. I'd only pick this over the Pro if the bridge is genuinely optional for how you live. Renters who never lock remotely will barely notice the gap. Frequent travelers will.

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