On Tue, 23 Aug 2011 17:10:10 +0100, wrote:


I have a mains powered - with 10-year lithium backup - interlinked
fire alarm system comprising of 3 off Optical Smoke alarms and 1 off
Heat alarm (for the kitchen)
I changed the 2 Ionisation alarms to optical on the advice of Kidde -
about 3 years ago after sporadic alarms occurred (usually in the early
hours of the morning) when there was no cooking/ironing/smoking or
anything triggering them.

That is rather odd advice, is the building two storey and where are
the alarms located?

Ionisation tends to give earlier warning of the most dangerous night
time slow start fires which emit no smoke in the early stages so are
usually preferred over optical for a sole alarm.

Now, here I am a further 3 years on and one of the 'new' optical
alarms has started the same game.

Spiders or other small insects setting up home inside them are a
common cause of optical alarms going off sporadically. This tends to
occur at this time of the year. Use a can of compressed gas (dust-off
or similar) to clean them out.

Batteries are temperature sensitive so when they start to fail they
will usually trigger the low battery (but usually not a full alarm)
early in the morning when the temperature is at its lowest. I
wouldn't expect that to be a problem at the moment unless nighttime
indoor temperatures where you are have been quite low. I assume the
interlink is by wire and not radio?

Does anyone else have this problem?

It isn't uncommon, having too many smoke detectors can be as dangerous
as having none - people get fed up with nuisance alarms and disable
them or ignore them. With one heat alarm over the cooker and one
ionisation alarms at the head of the stairs you have pretty good
cover. Bedroom sounders may be required if anyone in the house is
hard of hearing or habitually uses medication to help them sleep.

Should I expect the unit to need replacing at 3 yearly intervals? Each
alarm costs around £40 so this gets a fairly expensive hobby

There are a lot cheaper units around for example
http://www.tlc-direct.co.uk/Products/TLSD141.html

The Lithium battery isn't really required in owner occupied premises.
Alkaline will be just as good if you change the battery every year or
when it reminds you every couple of years by starting to beep (at
3AM!) .