Smoke detectors - wired or battery?

I'm sure the good folks of TZ can help me with this quandary...

I have a four storey town house with mains powered smoke detectors on each floor, so mains wiring to the detectors is already in place. They're 20 years old now and I should change them (although they do still work), but I'm wondering whether there's any advantage to having mains powered detectors these days?

You can get 10 year battery detectors that are a lot cheaper than the mains ones. Would these be okay, or is there a good reason to stump up for the mains one? Presumably mains + battery backup is the optimum?

Any advice gratefully received, if I can spend a little less and still keep the family safe then that would be nice...

I'm not sure many/any are actually mains now.

We have an ADT monitored alarm system, that includes smoke detectors, but all run from batteries now.

I'd just go with the battery ones.

Hmmm, we have an ADT monitored alarm as well. Didn't realise they could monitor the smoke alarms as well, will look into that.

Assume you have to use their specific alarms?

https://www.fireservice.co.uk/safety/smoke-alarms/

"Mains-powered alarms have to be installed in all new buildings and after a major refurb. Make sure that the chosen mains powered alarm has a battery back-up. These can be alkaline batteries (need annual changing) or the alarm can be supplied with re-chargeable lithium batteries, which will last the lifetime of the alarm. Mains alarms need to be installed by a qualified electrician."

Id say use mains powered ones if the cabling is there.

If the wires are there go mains with battery back up. Cheap as chips from screwfix.

We had our house redone two years ago and put mains powered ones in. You've already got power to them, you might as well use it.

We have an ADT monitored alarm. While the alarm (PIR) sensors are wireless, our 3 smoke detectors are mains. I feel happier that way (having seen too many smoke/carbon monoxide detectors over the years with dead or disconnected batteries).

Thanks chaps, good info.

An additional question, now that I've started looking into it: Thermally Enhanced, Optical, Ionisation sensors??? Is there a clear winner here, or is it marketing guff?

EDIT: Just found this:

Ionisation: These are the cheapest and cost very little to purchase. They are very sensitive to small particles of smoke produced by fast flaming fires, such as paper and wood, and will detect this type of fire before the smoke gets too thick. They are marginally less sensitive to slow burning and smouldering fires which give off larger quantities of smoke before flaming occurs. They can also be too over-sensitive near kitchens.

Optical: These are more expensive but more effective at detecting larger particles of smoke produced by slow-burning fires, such as smouldering foam-filled upholstery and overheated PVC wiring. They are marginally less sensitive to fast flaming fires. Optical alarms can be installed near (not in) kitchens, as they are less likely than ionisation alarms to go off when toast is burned.

So, it looks like Optical is better for my purposes.

In Essex the fire brigade come and fit smoke detectors free of charge. It’s done by office that are on light duties. Quick, friendly, fitted with no mess and free.

Sounds good - is that just for new installations, or even if you're replacing existing ones?

As stated above, local Fire Service will supply & fit free of charge to any property. It`s a Govt funded scheme to reduce fire related deaths. They should also have a quick look around the property and give free safety related advice. Even if you go with replacing your existing hard-wired with new, it wont hurt to have a visit for the advice. My local brigade would advise to stick with hard-wired.
Regards Daz, (recently retired Fireman).

Thanks all, a wealth of knowledge and experience here as always, much appreciated.

Bear in mind batteries on a monitored system will need changing at regular intervals,they won’t be cheap.Ex ADT engineer for what it’s worth.

The thing I like about the wired detectors in my parent's house is that if one goes off, they all go off. If it was a regular detector in one of the attic rooms and it went off and the door was closed, there is no way it would be heard in the living room, so they're pretty reassuring in a large house.

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Originally Posted by hafle

The thing I like about the wired detectors in my parent's house is that if one goes off, they all go off. If it was a regular detector in one of the attic rooms and it went off and the door was closed, there is no way it would be heard in the living room, so they're pretty reassuring in a large house.

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This. The interconnection you get with the wired alarms is a nice feature. Battery alarms can have wireless interconnection (like Nest) but i found when looking they were all a lot more expensive than the wired ones.

to be compliant don't they need to be wired in FP200 if you change them?

Our alarms are hard wired with battery backup inc the carbon monoxide one but our ADT smoke alarm which is central station monitored is battery but a PP9 the
same as a regular one, do the new alarm systems still have the great big battery on a domestic fit?

I would imagine your wired alarms will have a backing plate / base screwed to the ceiling, with the electrical wiring connections. The alarm itself will screw/twist/clip into the backing plate. It is highly likely you can buy replacement alarms that fit into your existing backing plates.

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Originally Posted by MadeOfCheese

Sounds good - is that just for new installations, or even if you're replacing existing ones?

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Why would you want to make your house less safe ?

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Originally Posted by Nogbad The Bad

Why would you want to make your house less safe ?

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Did you read the whole thread? I think he was asking about the FB doing it for free...

M

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Originally Posted by hogthrob

I would imagine your wired alarms will have a backing plate / base screwed to the ceiling, with the electrical wiring connections. The alarm itself will screw/twist/clip into the backing plate. It is highly likely you can buy replacement alarms that fit into your existing backing plates.

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This is what I did a couple of years ago when ours needed replacing, something like stick a screwdriver in to release a clip and twist.

MoC - We are in the same area aren't we? Only a 3 storey townhouse though, the poor side of town! Twisted one off, went to the local electricals supplier and bought three identical replacements. I don't think they were that expensve.

For existing properties, your local Fire Service will probably come and assess and fit battery ones for free (generally, 10 year battery life).

If you have an extension/loft conversion or significant building works done then Building Control will try and insist that you have a mains system. We opted for a Nest set up and it has been fine - mains with battery backup, notifications when away and it does a regular test and reports the result.

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Originally Posted by BillyCasper

MoC - We are in the same area aren't we? Only a 3 storey townhouse though, the poor side of town!.

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We are if memory serves, Teddington for me.

On closer inspection, my alarms are all Kidde Firex F1, which is a basic wired ionisation alarm. Although they all apparently still have a few years in them (although I can't for the life of me remember replacing them) I'm gonna swap them all out for Kidde KF20 which are the optical version.

Thanks again for all the advice.

When we have out loft extension (about 6 years ago) we had to have our fire alarms (4) connected to the mains - with battery back-up.

Building regs init gov.

Personally i would replace on a like for like basis.

Don't forget to look into carbon monoxide detectors.

^^^^^^^ Great point re carbon monoxide detectors

Hard wired with battery back up, no brainer

Have you considered smart smoke detectors? https://store.google.com/gb/product/...rotect_2nd_gen Combined smoke & carbon monoxide.

Nest Protect is great, no subscription needed and good support too. We installed 3 in the new house, came in tonight to be told politely ‘There is a problem with the Nest Protect in the Hallway’ which had list the ability to speak!

Ten minutes in chat with Nest and a new unit is being shipped within 2 days with a free return for the faulty unit too!


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I have a separate carbon monoxide detector, it sits next to the gas fire in the living room, I figure that’s probably the first place it’ll trigger.