My CO detector goes off for no obvious reason
Home Nura guide — category: Smoke & CO Detectors
Diagnosis
Warning: this symptom can point to a serious hardware defect. Stop using the device until you know the cause. We recommend contacting the manufacturer or an authorized repair service before you try to use it again.
What to do
Unplug it right away and stop using it. Document the symptom (photos, video, the sounds it makes), then contact the manufacturer's support team. Keep your proof of purchase handy: any warranty claim starts there.
Repair or replace?
If the problem is still there after these checks and the appliance is out of warranty, weigh the repair estimate against the cost of a new model.
If you're replacing it
Smoke & CO Detectors: the picks from our buying guide
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Best overall
Netatmo Smart Smoke Alarm
Certified to the European EN 14604 standard, hub-free and powered by a 10-year battery, it still sounds when your internet is down and works with Apple Home and Google Home.
Photo: © Netatmo
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Best value
X-Sense XS01-WX
An entry-level Wi-Fi alarm certified to EN 14604 that sends phone alerts with no hub, ideal for covering several rooms.
Photo: © X-Sense
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Best for carbon monoxide
Netatmo Smart Carbon Monoxide Alarm
Certified to the European EN 50291 standard, it monitors CO on a 10-year battery and alerts your phone: the essential add-on if you have a fuel-burning furnace, boiler or wood stove.
Photo: © Netatmo
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Other common problems in this category
These issues affect the same type of appliance — each one comes with a diagnosis and the steps to take.
- Smoke & CO DetectorsMy smart smoke detector chirps at random times
- Smoke & CO DetectorsHow long does a smart smoke detector actually last?
- Smoke & CO DetectorsThe monthly test on my smart smoke detector fails without an error message
- Smoke & CO DetectorsMy smart CO detector shows high ppm readings even with the furnace or boiler off
Frequently asked questions
Check the manufacturer's warranty first: how long it lasts and what it covers vary by brand and model, so read the terms for yours and keep your proof of purchase. If you bought it new in the EU, a two-year legal guarantee also applies (Directive (EU) 2019/771), covering defects present at delivery, whenever they first show up.
If you're still within the seller's return window, a return or exchange is usually the fastest fix. After that, go through the manufacturer's support team: it handles warranty claims and can often repair the unit even after the warranty has run out. Either way, keep your proof of purchase.
Our public methodology lowers the Nura Score /10 of any model in our Smoke & CO Detectors guide whose recurring failures show up in owner reviews. A model that breaks down too often never makes it to the top, whatever the brand.
Generally, yes, if you stick to routine maintenance: cleaning, replacing a gasket, recalibrating. Irreversible changes to the hardware are what can cause problems, so read your warranty terms before you open anything up. Anything the manufacturer's manual walks you through is the safe zone.
Your proof of purchase, the exact model name and a record of the symptom: photos, a short video, the sound it makes and any error code. Note when the problem started and what you've already tried. With all that in hand, support can pin down the problem much faster.