Smoke gets in your eyes...
July 19, 2010 3:17 PM   Subscribe

Are there any issues replacing an old AC-powered smoke alarm with a newer alarm?

I have a fairly old (15+ years, if not more) First Alert smoke alarm on the ceiling in the hallway outside the bathroom. It plugs into a 110V line in the ceiling through a crimped-on connector, black and white for power and red for communication.

When I take a shower, steam leaves the bathroom and sets off the smoke alarm in that hallway.

I'd like to move the alarm further down the hallway.

It is also an old alarm and does not have a 9V battery backup.

I bought a Kidde alarm with the intention of replacing the old unit, but the power connectors do not match.

My questions are:

1. Can I crimp on a Kidde or other battery-backup AC-powered smoke alarm on the same power line that feeds the current smoke alarm?

2. If I do so, do I need to replace all the other smoke alarms on the same power line with the same model of new alarm, to ensure communication?

3. Are there smoke alarms that perform better (i.e. do not go off) around light steam?

4. Do I dispose of the old smoke alarm at a haz-mat dump?

Are there any other questions I forgot to ask about setting this up? Thanks for your advice.
posted by Blazecock Pileon to Home & Garden (4 answers total) 1 user marked this as a favorite
There are codes requiring how close to certain rooms (kitchen, bedroom) smoke alarms have to be. Check to make sure your new placement won't violate any of these.
posted by brainmouse at 3:37 PM on July 19, 2010

We had a similar issue with a shower setting off an old smoke detector right outside the bathroom. Replacing with a new smoke detector in the same location solved the problem. I think it was a symptom of a smoke detector that needed to be replaced.

As for the compatibility issue, if your other smoke detectors are more than 10 years old, they should also be replaced anyway, because the sensors wear out over time. I would think you should be able to buy connectors for your new Kidde detector(s), if they didn't already come with them.

We were unable to get our local hard-to-recycle center to take the old smoke detectors--they told us to throw them in the garbage, which surprised me. So check with your local trash service or hazardous waste center.
posted by partylarry at 4:35 PM on July 19, 2010

Best answer: Some detectors are connected together, so that setting one off triggers all the other alarms in your house. They do this via a separate signal wire, in addition to the AC power connections. I've never lived in a house that had this "feature" (which I think would probably be obnoxious), but if yours does, and if you want to keep it working, you'll have to relocate the messenger wire from the old location to the new one.

Some new detectors do the communication thing wirelessly, but you have to buy all new detectors of the same brand.

There's no reason why you can't take off the old power connector and put on the new one's connector. Fundamentally, installing a smoke detector is no different than installing a light fixture. You just connect the black to the black and white to the white and green to the green (if it has one), except instead of wiring directly to the detector, you generally wire to pigtails connected to a removable plug.

If you don't want to rewire the plug, you can get universal-fit (or purportedly 'universal' anyway) detectors that take multiple brands' plugs, so you can use the existing one from your old detector. However ... I've found that some detectors in my house are so old (probably vintage 1980 or so) that even the universal-fit ones don't fit.*

Also ... although you may already know this, there are two types of smoke detector in common use. One is photoelectric, the other is ionizing. The photoelectric type just looks for smoky/cloudy air, the ionizing type actually looks for smoke particles. It may be that changing from one type to the other, while keeping the detector mounted in the same place, reduces the number of false positives you get from your shower. I'm not sure which type would be more or less susceptible to water vapor, but if you have one you might want to try the other for a while, and if it doesn't work you can always resort to moving it up the hallway then.

* The old ones in my house actually had a male card-edge connector on the detector, which slid into a female edge connector on the base, which was the part attached to the wall. I've never seen any modern detector like this; they all use the little removable plugs.
posted by Kadin2048 at 5:29 PM on July 19, 2010

Response by poster: Also ... although you may already know this, there are two types of smoke detector in common use. One is photoelectric, the other is ionizing

I installed a photoelectric model in the same place as the old unit, and no more false alarms from shower steam. Thanks for the tip.
posted by Blazecock Pileon at 1:35 AM on July 23, 2010

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