Home Security and Safety - Maintaining and Replacing Your Smoke Alarm
Smoke alarms can be lifesavers in the event of a fire. They mightn't
stop your home from burning down, but they provide the extra few minutes
of time during which you can exit the house.
There are two types of alarm, ionization and optical. Ionization alarms
which use a small radio-isotope source, are best at detecting the small
particles produced by a flaming fire. Optical smoke alarms are better at
responding to the relatively larger smoke particles generated by a
Ideally you should have at least two alarms, one upstairs and one
downstairs in a two-story home. Having two alarms is added insurance so
that if one fails, the other acts as a backup. For added safety, an
ionization and optical alarm can be installed side by side. Alarms
should be located so that they are not subjected to draughts which could
prevent smoke reaching them. So the best place is away from windows and
doors. Also they should be kept away from corners of rooms and at a
minimum distance from the point at which the wall reaches the ceiling.
This is because smoke doesn't easily move into these "dead spaces".
Consult the instructions provided before installing.
What about batteries? Well you should use alkaline types which have a
long shelf life and higher capacity than zinc carbon or zinc chloride
types. Avoid buying batteries in bargain basement shops unless the word
"alkaline" is printed on the pack. Terms such as "high capacity" or
"super heavy duty" are meaningless and the batteries may not be
alkaline. Check the best before date also. Alarms usually require a 9v
square PP3/MN1604/6LR61 type. If you use a rechargeable type, the
voltage is lower (8.4v nominally) and the alarm might not work
correctly and/or the low battery warning may not operate. Also re-chargeables have the annoying habit of self
discharging and will need to be recharged. Alkaline batteries usually
last at least one year in an alarm but may last 2 to 3 years. Check the
alarm regularly by pressing the self test button.
Do alarms ever need to be replaced? Yes, according to the NFPA, alarms
should be replaced every ten years. Life span is limited and
accumulation of dust, dirt and general grime can interfere with the
alarms ability to detect smoke.