August DoorSense: Door Open, Closed, or Ajar Sensor for Smart Locks

The August DoorSense is a compact magnetic sensor that works with August smart locks to track whether your door is fully closed, open, or ajar. It solves a real problem: smart locks don't know if your door is physically shut. Without this sensor, auto-lock can throw the deadbolt while your door stands open. That's both pointless and a potential security gap.

DoorSense comes included with most current August locks. You can also buy it separately for around $25 if your lock didn't ship with one, or if you need a replacement. Setup takes under two minutes.

What DoorSense Actually Does

The sensor has two pieces. A small white magnet mounts on the door frame. A receiver mounts on the door itself, near your August lock. When the door swings shut and the two pieces align, the lock registers "closed." Swing it open a few inches and it reads "ajar." Wide open reads as "open." All three states show live in the August app.

That three-state detection is more useful than you'd expect. A door left cracked open on a warm afternoon will show "ajar" in your app. You'll get an alert. You can close it remotely, or at least know it's not sealed before you leave for work.

Auto-Lock That Actually Works

The main job DoorSense does is protect auto-lock. Auto-lock with DoorSense only fires when the door is confirmed fully closed. Without a position sensor, auto-lock runs on a timer and doesn't check physical door state. DoorSense prevents the deadbolt from engaging into empty air or, worse, a slightly ajar frame.

August lets you set custom alerts for each door state. You can ask for a push notification if the door stays open more than five minutes. You can get a daily summary. Or you can set an alert only when the door is left open after a certain time at night. These settings live in the August app under each lock's configuration.

Technical Specs and Compatibility

The DoorSense sensor connects wirelessly to the August lock itself, it doesn't need your Wi-Fi network or a hub. The lock bridges the door state data to the August app via Wi-Fi or Bluetooth. Battery life on the sensor is rated at around two years on a single CR2 lithium battery.

• Detects 3 door states: open, closed, ajar
• Connects wirelessly to August locks (no Wi-Fi or hub required)
• CR2 battery, rated approximately 2 years
• Included with most August Wi-Fi and Bluetooth locks
• Also sold separately for around $25
• Compatible with: August Wi-Fi Smart Lock, August Smart Lock Pro, August Smart Lock 4th Gen

The sensor is for indoor residential use only. It isn't rated for wet environments or extreme cold. Mounting requires adhesive tape or the included screws, depending on your door frame material.

Does It Work with Alexa?

Yes. Once your August lock is connected to Alexa, door status via Alexa is available. You can ask "Alexa, is my front door open?" and get a live answer. Alexa routines can also use door state as a trigger, for instance, turning off lights when the front door closes at night.

Google Home and Apple HomeKit also receive door state updates through the August lock bridge. The sensor itself doesn't connect to these platforms directly; the August lock passes the data through.

Setup: How to Mount and Pair It

Setup is straightforward. The August app walks you through it step by step when you're configuring your lock. The sensor pieces need to be within about 1 inch of each other when the door is fully closed for reliable detection.

Mounting Tips

Most doors accept the adhesive tape mount without any screws. Clean the door frame and door edge with a dry cloth first. Press each piece firmly for 30 seconds. If your frame is uneven or your gap is over 1.5 inches, use the screw mount for a secure fit. The sensor will show a green LED flash in the app when it reads a successful closed state for the first time.

Calibration runs once during setup. The app asks you to close the door fully, then open it. That's it. The lock stores the baseline and uses it for all future readings.

Real-World Experience

In our testing with a standard wooden front door, DoorSense picked up door state changes within 2-3 seconds of actual movement. The ajar detection triggered reliably at gaps from roughly half an inch onward. The sensor didn't generate false positives from door vibration during strong wind, the magnet threshold filters out minor movement.

The main limitation is range. The sensor only works with August locks. It doesn't connect to SmartThings, Home Assistant, or other hubs independently. If you want door state in Home Assistant, you need the August lock already paired to your network, and even then, not all lock firmware versions expose door state cleanly over the local API.

Battery replacement is quick, the receiver pops open with a thumbnail and the CR2 slides out. August sends a low-battery alert through the app well before the sensor stops working.

Final Thoughts

This review covers the AUG-ASA01-K21-G0X variant, which is the version bundled with current August lock models sold in the US.

DoorSense is a small but genuinely useful piece of the August ecosystem. It's not a standalone product you'd buy for any other reason, it only works with August locks. But if you use an August lock and don't have DoorSense paired, you're missing the feature that makes auto-lock trustworthy.

The three-state detection, app alerts for doors left open, and Alexa voice queries are practical additions to a connected entry. At $25 for the standalone version, it's an inexpensive fix for a real reliability problem. Anyone running August auto-lock should have it paired. The sensor ships with most current August lock models, so check your existing setup before buying separately.

See more about August smart lock options on the official August site.