What Does the Door Sensor Do?
It does one thing: it tells your Nuki Smart Lock whether the door is physically open or closed. That is it. No motion detection, no camera, no temperature readings. Just a two-piece magnetic sensor — one part on the door frame, one on the door — that reports open/closed state to the lock via Bluetooth.
This enables "lock when door closes" automation. Without the sensor, the Smart Lock can only auto-lock after a timer (say, 20 seconds after locking). The problem with timer-based auto-lock: if the door is still open, the lock turns the cylinder into a closed door — the deadbolt extends into thin air, and you have to manually retract it before closing. With the sensor, the lock waits until the door is actually shut, then locks. No more deadbolt-into-air situations.
How It Works with Your Smart Lock
Once paired via the Nuki app, the Door Sensor shows door state in real time. The app displays "Door open" or "Door closed" alongside the lock state. The activity log records every open and close event with timestamps.
The primary automation is straightforward: door closes → lock engages after a 1-second delay. You can adjust the delay or disable the automation entirely. There is no complex rule engine — it is a binary trigger.
For security-conscious users, the activity log is genuinely useful. You can see exactly when your front door was opened and closed throughout the day. If you have a cleaner, a dog walker, or kids coming home from school, the log shows their arrival and departure times. It is not a replacement for a camera, but it answers "has anyone been at the door?" without one.
Installation
Installation takes about 30 seconds. The sensor is magnetic — one piece sticks to the door frame, the other to the door, aligned within about 15mm of each other. Nuki includes 3M adhesive strips. No drilling, no wiring, no tools.
The sensor is small (about the size of a USB stick) and nearly invisible once mounted. It works on wood, metal, and composite doors. The adhesive has held firm for six months on a painted wooden frame — including through humid Dutch summers. If the adhesive ever fails, you can use the included screws instead.
One caveat: on metal doors with metal frames, the magnet alignment can be finicky. You may need to test a few positions to get reliable detection. On wooden doors, it works perfectly on the first try.
Do You Actually Need One?
Honest answer: most people do not. If you use Auto Unlock (the lock opens when you approach), you probably close the door behind you and it locks automatically after a timer. That workflow works fine 90% of the time.
The Door Sensor earns its keep in three scenarios. First, if you have family members (especially children) who sometimes leave the door ajar — the sensor ensures the lock only engages when the door is fully closed. Second, if you want an activity log of door opens and closes for security awareness. Third, if timer-based auto-lock has ever caused the deadbolt-into-air problem for you, the sensor eliminates it permanently.
At €59, it is not expensive, but it is also not essential. Buy the Smart Lock and Keypad first. If you find yourself wishing the lock knew whether the door was open, add the sensor later.