Trying not to burn down my house

[Clive George]

Guess which bit of electrical kit in my house has the scorch marks from an overheating electrical connection?

Yup, the smoke alarm. I think the pin wasn't mounted to the board very well.

Firex FADC230

Any preferred replacements? Mains/battery, ionising detector, mounted to a batten on the ceiling, so no tricky bits. Screwfix have a "Dicon", a "Fireangel", and a "Firstalert" - the latter two are 10 year battery models. I see my Firex has a 10 year life despite being mains powered - I guess this is supposed to be the lifetime of the radiation source.

[Matty F]

The half life of Americium-241 is 432 years, so it should outlast the house.

[Andrew Gabriel]

The life is more to do with inaccessible parts becoming too dirty, and affecting operation (leakage of the ionisation current causing a false alarm and/or obscuring of the cell causing delayed/no alarm). However, as time increases, I guess there's also increasing chance of electronic failure having happened, as in the OP's case.

The 10 year batteries are lithium (but usually not changable). You can buy lithium PP3's to put in any PP3 battery model.

[Steve Walker]

I've never seen the point in the alarms with fixed batteries, unless it is to prevent people taking the batteries out because of nuisance alarms. If that is the case, they'll simply throw the whole thing away or pull connections out!

Our alarms have replaceable batteries, a simple button test and if the battery gets low, the alarm starts beeping at irregular intervals - although it can take a few days to work out what's beeping, as they are so infrequent and we have many other things, including children's toys that beep.

SteveW

[Andrew Gabriel]

It's because research shows a significant proportion of battery alarms never get the battery replaced, so after the first year, they sit there disabled.

Mine are all PP3 replaceable battary types, but they all have a PP3-sized module in them which powers them from the 12V burglar alarm, and generates a signal back to the alarm when they start drawing enough power for the sounder. So I never have to change any smoke detector batteries.

When I put some in my parents' home, I fitted them with the lithum (10 year) PP3s, so we don't have to arse around with battery changing. Since then, they've had an extention and also have mains interlinked ones, but I didn't bother removing the battery ones.

[Gel]

Replace with A firex 4870 or 4973 (optical); try TLC or QVS websites

[ARWadsworth]

I am surprised there were any scorchmarks due to the very small current that is used.

A direct replacement is probably the easiest and having fitted hundreds of these alarms I can assure you that it is not a known problem.

Adam

[Clive George]

Me too. But it is nicely brown, and the relevant pin did fall out when I touched it.

Thanks.

[ARWadsworth]

Bloody hand fisted electricians that cannot do their job properly when installing them:-)

Adam

[ARWadsworth]

SteveW

That is fine for you and me, but there are a significant number of people who will remove batteries when they go flat and do not replace them, they will also remove batteries for kids toys and not replace them or they cannot afford to replace the batteries when needed.

Adam

[Dave Liquorice]

A few watts in a place that isn't supposed to have any disipation will "age" that place quite quickly. You only need 4mA @ 240v to dissipate 1W.

[Steve Walker]

Yes, but the end result is that if they're doing anything which keeps falsely triggering the alarm, they'll throw probably take the whole alarm down and never put it back. At least with the removeable battery type, I can whip the battery out and leave the cover hanging down to remind me to put it back when I'm done!

SteveW

[Dave Liquorice]

Aye, and sensible removable battery ones don't allow the cover to clip back in place unless there is a battery fitted.