Everyone Does This
Studies suggest that around 30% of people regularly experience doubt about whether they locked the door. For most, it's a fleeting annoyance — a 30-second mental replay that confirms yes, you locked it. For others, it's enough to turn the car around and drive home to check.
The cost of this anxiety isn't just mental. If you go back to check, that's 20–40 minutes of your day gone. If you don't go back and the door actually is unlocked, you spend the whole day worrying. And if something happens — a break-in, a pet getting out, rain through an open door — the consequences are real.
This isn't about being forgetful. Locking the door is an automatic action, and automatic actions are exactly the kind of thing your brain doesn't bother recording clearly. You lock the door the same way every day, which is why you can never remember whether today's lock was real or a memory of yesterday's.
Checking Without Going Back
Without a smart home setup, your options are limited. You can call someone who's still at home and ask them to check. You can check a security camera if you have one pointed at the door. Some people text their partner or housemate: "did you lock up?"
All of these are workarounds. They depend on someone else being available, or on having installed a camera (which costs money and only shows you the outside of the door — you can't tell from a camera feed whether the deadbolt is engaged). What you actually want is a definitive answer: is my door locked right now, yes or no?
The Real Fix: Door Sensor + Smart Lock
A smart lock with a door sensor solves this completely. The door sensor (a small device mounted on the door frame) detects whether the door is physically closed. The smart lock knows whether the deadbolt is engaged. Together, they give you a definitive status: door closed and locked, door closed and unlocked, or door open.
You can check this status from the app on your phone at any time. No calling anyone, no guessing, no driving back. Open the app, see the status, move on with your day.
But the real fix is auto-lock. Configure the smart lock to automatically lock the door a set number of seconds after the door sensor detects it's been closed. Typical settings range from 5 to 60 seconds. Once you set this up, the question "did I lock the door?" becomes meaningless — because the door always locks itself.
How Nuki Handles This
Nuki's Door Sensor 2.0 attaches to your door frame with adhesive — no drilling, no wiring. It communicates wirelessly with the Smart Lock and detects door open/close states.
When you enable Auto Lock with the door sensor trigger, here's what happens: you leave the house, pull the door shut, and the sensor detects the door is closed. After your configured delay (say, 20 seconds), the smart lock automatically engages. You get a push notification confirming the door is locked.
From the app, you can see the live status at any time: a green icon means locked, an orange icon means unlocked, and a red icon means the door is open. No ambiguity, no checking behavior, no driving back home.
You can also set up alerts for unusual states — for example, get notified if the door has been unlocked for more than 5 minutes, or if the door is open past 11 PM.
Auto-Lock Settings
Nuki offers three Auto Lock trigger modes. The first is time-based: the door locks automatically X seconds after being unlocked, regardless of the door sensor. Good for back doors or garage entries where you might not install a sensor.
The second is door-sensor-based: the door locks X seconds after the sensor detects the door has been closed. This is the most popular option because it only locks when the door is actually shut — preventing the embarrassing scenario of the deadbolt engaging while the door is open.
The third is manual: Auto Lock is off, and you lock via the app, keypad, or physical key. Some people prefer this for specific doors where they want full manual control.
Most users start with a 20-second delay on door-sensor mode and adjust from there. If you have kids running in and out, you might increase it to 60 seconds. If you live alone, 10 seconds works fine.