A contact sensor can misread when magnet alignment, gap, orientation, battery or mounting has changed. Move the magnet near the sensor before deleting it from the system. Watch the live status while slowly bringing the magnet to the marked side of the sensor.
Differential
Likely causes of “Door or window sensor says open when it is closed”, and how to tell them apart
- 1
The magnet and sensor are too far apart or misaligned
What separates it The status flips only when the door is pushed shut hard, and the gap between the magnet and sensor is bigger than the maker's limit.
How to confirm Watch the live status while slowly bringing the magnet to the marked side of the sensor.
- 2
The battery is low
What separates it The sensor reports open or unavailable intermittently and the battery level shows low.
How to confirm Replace the battery with the specified type and test again.
- 3
The magnet is on the wrong side or the door has warped or settled
What separates it The sensor worked until the season or the door frame changed, and the alignment shifted.
How to confirm Check the alignment marks and the gap when the door is fully closed.
- 4
The sensor has lost its connection to the hub
What separates it The status is stale, the app shows an old time and the sensor is far from the hub.
How to confirm Check the sensor's last update time and its signal to the hub.
Before you touch a setting
Record this first — changing settings destroys the evidence
- The status shown live as you move the magnet toward the sensor.
- The gap between the sensor and the magnet when the door is closed.
- The battery level and the sensor's last update time.
Try in this order
0 of 4 completedCapture the exact symptom
ReversibleWatch live status while slowly bringing the magnet to the marked side of the sensor.
Run the smallest isolation test
ReversibleReplace the battery if low and realign within the specified gap using temporary tape for testing.
Correct only the proven cause
ReversibleRemount securely after confirming the exact alignment; re-pair only if the sensor never changes state nearby.
Verify before changing anything else
ReversibleOpen and close ten times and confirm automations receive every event.
Stop boundary
When this stops being a self-service repair
- !Re-pair the sensor only if it never changes state when the magnet is next to it, because re-pairing removes it from automations.
Evidence ledger
Sources behind this answer
Exact questions
Common questions
How close does the magnet need to be to a door sensor?+
Each maker gives a maximum gap, often a centimetre or two. Use the figure in your manual and mount the parts on the marked sides.
Why does the sensor say open when it is closed?+
Magnets and sensor halves may be too far apart, misaligned or the battery may be weak. Check the gap between the two parts.
What should I try first?+
Realign the magnet and sensor, clean them and replace the battery.
Could the sensor be on a warped door or window?+
Yes. Seasonal movement can change the gap, so adjust the position or use the sensor's spacing guidance.
Should I re-pair it?+
If the app still shows the wrong state, remove and re-add the sensor.