Are you sure?
http://www.safety-council.org/info/home/smalarm.htm
... Smoke alarms can be electrically powered, battery powered,
or a combination of both.
http://www.ibc.ca/homeauto_homeinsure_smokealarm.asp
... You should also test your alarm monthly to make sure it's working. Use
a candle, cigarette, or incense to introduce smoke into the alarm until it
sounds. If the alarm is battery-powered and doesn't sound, replace the
battery and try again. If it's electrically-operated and doesn't sound,
check the fuse and try again. In either case, if the alarm still isn't
working, replace the unit. A dead unit is worse than none at all, as
it can give you a false sense of security.
Saanich BC Smoke Alarm Bylaw No. 7126:
... Smoke alarms installed pursuant to this bylaw may be battery powered
or connected to an electrical circuit... Where the owner installs an
individually battery powered smoke alarm, the owner shall install new
batteries in the alarm at least once every twelve months.
And finally, your Queen
http://www.hc-sc.gc.ca/iyh-vsv/prod/detect_e.html
Smoke Detectors
(c) Her Majesty the Queen in Right of Canada,
represented by the Minister of Health, 2004
... Change the batteries as often as recommended by the manufacturer.
Nick