jadnashua said:
I've seen wired detectors both with and without battery backup. A battery backup is always a good idea, but if you don't have one, I still think it's a good idea to have it on its own circuit. If you use a lithium backup, and don't have too many power outages, it could last the life of the detector (10-years as recommended by the fire codes).
Here is what the IRC has to say about the power supply to smoke alarms no matter what anyone's idea is.
SECTION R313
SMOKE ALARMS
[F] R313.1 Smoke alarms. Smoke alarms shall be installed in
the following locations:
1. In each sleeping room.
2. Outside each separate sleeping area in the immediate vi-
cinity of the bedrooms.
3. On each additional story of the dwelling, including base-
ments but not including crawl spaces and uninhabitable
attics. In dwellings or dwelling units with split levels and
without an intervening door between the adjacent levels,
a smoke alarm installed on the upper level shall suffice
for the adjacent lower level provided that the lower level
is less than one full story below the upper level.
When more than one smoke alarm is required to be installed
within an individual dwelling unit the alarm devices shall be in-
terconnected in such a manner that the actuation of one alarm
will activate all of the alarms in the individual unit. The alarm
shall be clearly audible in all bedrooms over background noise
levels with all intervening doors closed.
All smoke alarms shall be listed and installed in accordance
with the provisions of this code and the household firewarning
equipment provisions of NFPA 72.
[EB] R313.1.1 Alterations, repairs and additions. When
interior alterations, repairs or additions requiring a permit
occur, or when one or more sleeping rooms are added or
created in existing dwellings, the individual dwelling unit
shall be provided with smoke alarms located as required for
new dwellings; the smoke alarms shall be interconnected
and hard wired.
Exceptions:
1. Smoke alarms in existing areas shall not be re-
quired to be interconnected and hard wired where
the alterations or repairs do not result in the remov-
al of interior wall or ceiling finishes exposing the
structure, unless there is an attic, crawl space, or
basement availablewhich could provide access for
hard wiring and interconnection without the re-
moval of interior finishes.
2. Repairs to the exterior surfaces of dwellings are ex-
empt from the requirements of this section.
R313.2 Power source. In new construction, the required
smoke alarms shall receive their primary power from the build-
ing wiring when such wiring is served from a commercial
source, and when primary power is interrupted, shall receive
power from a battery.Wiring shall be permanent and without a
disconnecting switch other than those required for overcurrent
protection.Smoke alarms shall be permitted to be battery oper-
ated when installed in buildings without commercial power or
in buildings that undergo alterations, repairs or additions regu-
lated by Section R313.1.1.