Posts from — June 2009

My electrician, who is safety-conscious above all else, has been bugging me for years now about smoke alarms. Sure, I have several battery-powered smoke alarms up, but from a safety improvement per dollar spent perspective, one really wants smoke alarms that are:

• hard-wired, with
• battery backup, and
• interconnected

The batteries in battery-powered smoke alarms will run out. They do chirp to let us know it’s time to change the battery, but more often than not I won’t have a spare battery handy, or I won’t have a step stool nearby, or it will be the middle of the night, so instead of going back on the ceiling with a new battery like it’s supposed to, the alarm will sit around on a counter, battery-less, sometimes for weeks. Hard-wired smoke alarms solve the dead battery problem because they draw their power from the house electrical wiring. As it turns out, electrical fires that disrupt the power before smoke could be detected are really rare, and our power is pretty reliable, so the risk that the power’s off when the alarm needs to sound is really quite small, smaller than the risk that your battery-powered alarm will be sitting, battery-less, on the counter. And most hard-wired alarms also have battery backup, so you’re covered during power outages, too.

There are two smoke-detection technologies: ionization and photo-electric. Ionization sensors do well with small smoke particles, from fast-burning fires, while photoelectric sensors do better with large smoke particles from smoldering fires. Most safety recommendations (including Consumer Reports) are reluctant to specify one as being a better choice, and recommend both. So add to our wish-list:

• dual-sensor

Interconnection of smoke alarms means that when one alarm goes off, all of them sound. So if there’s a fire in the basement while you’re asleep, the alarm in your second-floor bedroom will also go off, giving you much more time to escape than waiting either for enough smoke to set off a second-floor alarm or for you to hear the far-away alarm. The interconnection is conventionally done with three-conductor wiring: all the smoke alarms need to be installed on the same circuit and the third wire is used as the alarm interconnection signal wire. This is easy in new construction but really hard to retrofit: getting a new circuit to the ceiling of every location for a smoke alarm would mean lots and lots of holes in the walls and ceilings.

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