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DETA smoke alarm fault

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Hi All

I have three smoke alarms in the same circuit in the house. Two of these alarms have recently illuminated red and the other is still green. I have tried changing the backup battery on both of these alarms but still the alarms illuminate solid red. I’ve checked the supply and there is definitely a supply to both alarms. The alarms aren’t making a noise unless you press the test button and they work fine but both red lights will not clear? 

Any advice would be appreciated. 


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Good morning,

These DETA models are quite old now and have been discontinued. It is likely that they have exceeded their 10 year lifespan and have either developed a fault or the smoke detection chamber is too contaminated to be safe. Over time the alarm's sensor will degrade and its performance will be affected as dust and even small insects collect inside the chamber making it harder to detect actual smoke if there is a real fire. Because of this most manufacturers give an estimated lifespan of 10 years for domestic alarms, which should be shown as a replacement or expiry date on a sticker on the alarm - in the case of these DETA models it will be on the back where the power connector is.

Gently cleaning the alarms with your vacuum cleaner and its soft brush attachment may temporarily resolve the issue if it is caused by contamination. However, if the replacement date has been exceeded then we strongly recommend replacing the alarms even if vacuuming them seems to resolve the red light problem.

The sticker on the back will also show you the exact model number and type of alarm you have, to help you find the most suitable replacement. While that particular range from DETA is no longer available, they were actually made by BRK who still make compatible alarms which you should be able to simply swap out on your existing base plates without having to change any wiring. You can find these replacement alarms here:


Daniel Bennett

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  • 6 months later...
Guest Thank you

Hi Daniel, Camd1994

Thank you so much for posting this - we had exactly the same problem and it's been very frustrating working out why the red light won't go off even though our expiry date is 2025.

Despite all efforts to clean it and replace battery - we have ordered a replacement.

Best regards


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  • 4 weeks later...

It is worth checking that you do not have another alarm (Smoke or carbon monoxide) nearby or in a drawer / top of a cupboard as beeping every 90 seconds does indicate low battery, but you have to change the battery in the correct device. Often there have been posts similar to yours and they post back saying they "found an old device hiding with a low battery"

If it helps I have been called to more than one case where the smoke alarm is beeping, only to find it is the smoke alarm beeping, but not the suspected one, but one further along the hall that is beeping. (Not found one in a drawer, but I have found one on top of a cupboard)

If you are sure it is your smoke alarm, make model and age would be useful.

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