Ah - she's like my wife, who uses the Girl Guide method.. "When it's brown it's cooking, when it's black it's done." along with a belief that a sausage is of no use unless you can sketch with it.
It's a *vague wooly remembrance* a watch crystal on the board that counts down to give it built in obselence.
I use Duracell, the cheap ones just don't last.
For sure (and I'll have to note whether it's taken into account leap years when it does eventually die :-) but I was curious as to *why* - there must (assuming the manufacturer isn't just pulling a fast one) be something that degrades in the sensor that necessitates a separate clock to 'brick' the detector after a pre-determined lifespan rather than risking it silently failing.
I like Bob's point of oxidisation - seems sensible (although I would expect that to be affected by environmental conditions - which might mean that the 7 year span is rather conservative for a lot of situations)
cheers
Jules
I'm sure that's true. 7 years would be the minimum usable life under relatively adverse conditions. But no easy way of detecting how 'worn' it is, so I guess that's why the chip.
The first CO sensors lasted a year, or until you poisoned them, e.g. by using an airosol furniture polish nearby. They have slowly improved but they are still subject to limited life and poisoning.
For ionisation smoke detectors, the sense current is so tiny that in many models that leg of the IC is bent up and not even soldered to the circuit board, as the PCB leakage would be too high. Eventually dust which settles in it will stop it working. They generally recommend
10 years max, although I have some significantly older which still work.On 06/01/2011 19:16, pete wrote: ...
I've got one of those that was supplied and fitted by the Fire Brigade. Four years later, it is sitting in a shed chirping away to itself.
Colin Bignell
Fantastic. Thanks a lot Mike: bookmarked that site now!
John
There's actually more chance of dangerous CO levels during a power failure, due to the use of LPG, oil, etc. in backup equipment.
and during the 1970's rolling power cuts, more risk of fire due to use of candles (and I don't think any domestic smoke detectors back then). I'd like to think most people have safer sources of backup lighting nowadays.
Well - I've got two Tilleys (bought from a couple who bought them for the miners' strike and didn't know how to use them), three Optimus lamps, a Bialladin or two...
I'd be surprised if many do.
More people use candles for decoration and haven't been taught to do so safely.
Owain
I know a guy who had a house transported to a remote island. He had a kerosine Primus stove. The valve in the pump got blocked by bits of leather (as it does). He had pumped the stove up, and a jet of kerosine come out of the pump and made a pool on the floor which caught fire. He didn't think or have time to release the pressure. There was no fire brigade on the island.The house completely burned down.
I've found the ionization-type smoke alarms get more sensitive as they age and I have replaced all my alarms well before their suggested lifespan due to the frequent false alarms.
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