|What are we talking about?
||How long does it typically take to install
a smoke alarm?
Around an hour (mains). Battery alarms a few minutes
||Alarm types - see comments
|Questions to ask
||Type of alarm(s) required which depends on location.
Battery (need replacing or 10 year) or mains powered with battery
back up. See comments
There are two types of smoke alarms in general use:
- Ionisation: These are the lesser cost and most common. They
are suitable for general and bedroom use and respond quickly
to fast flaming fires as they detect the invisible parts of
combustion gases. They will however alarm with particles given
off by cooking so are not suitable for use in locations in or
adjacent to kitchens.
- Optical (photoelectric): These cost a little more, detect
larger particles of smoke and hence are more suitable for general
use and near but not in kitchens as they are less prone to nuisance
alarms. They are not so good at detecting fast flaming fires
that give off little smoke.
Other alarms that will be found:
- Heat: These respond to heat only and can be used in kitchens
- Multi-sensor: these combine the ionisation and optical facility
and have a higher level of tolerance to cooking fumes and steam
- Carbon monoxide: these are not smoke alarms. They may be used
in addition to smoke alarms for detecting fumes from boilers
Some alarms have additional facilities, such as emergency lights
and silence buttons, for use where false alarms can be a nuisance
e.g. when cooking. Alarms specifically designed for the deaf are
In a standard smoke alarm, the alkaline battery will need to
be replaced every 12 months or so - the alarms usually emit a
steady beep when the battery is low. Alarms fitted with 10 year
lithium batteries are available. The advantage is that you don't
have to replace the battery every year but the alarm has to be
thrown away when the battery looses its charge.
Mains-powered alarms eliminate the problem of checking the battery
but to be safe need a battery back-up and need to be installed
by an electrician. They are typically fitted near a lighting ceiling
rose which is used as the power source.
Many alarms are now interconnected, meaning that if one alarm
is set off they all sound. In a 'new build' house or when rewiring
an existing property a cable can be run between alarms to provide
the interconnect. This is possible but not easy when fitting in
an existing property - it usually results in exposed cable or
trunking. To get over this problem radio bases are attached to
each alarm so they can talk to each other wirelessly. These need
mains power, usually from a lighting ceiling rose with the radio
base and alarm being fitted nearby so cable can be run in the
ceiling void. They also need built in battery back up.
Alarms that plugged into a light socket were available. They
used a rechargeable battery which charged up when the light was
turned on. The problem was that you need to make sure the light
was turned on often enough so carried a degree of risk. They are
seemingly no longer available.