AC Pwr'd Smoke Alarm--False Alarms?

Old 01-20-04, 02:47 AM
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Unhappy AC Pwr'd Smoke Alarm--False Alarms?

Hi All:

This is my first post, although I've lurked here before--great site! Sorry to come, hat in hand, with a problem, for my first post.

We have a BRK Electronics "AC Powered Ionization Smoke Alarm with Battery Back-Up" system in our house, which we've lived in for two years. It was installed by the previous owners in a major remodeling, in 2000. No problems to date.

Tonight, we're not sleeping because the smoke alarms are randomly going off for a couple of blasts, sometimes more, sometimes less. It's not the "low battery chirp" warning either; rather, it's the full alarm howl, but it starts with one or two blasts, then more, just like if there's actual smoke in the house.

This four bedroom house is an 1890's 2-story farmhouse, (cellulose insulation in attic) remodeled to an open plan downstairs (only). We have six interconnected smoke detectors, which each take a 9v battery as back-up. As I say, they're interconnected in that triggering one triggers the rest in a few seconds. They're also interconnected, obviously, by virtue of all being on the 110v house power.

They are going off like a normal smoke-triggered warning, i.e., first one unit will make one or two blasts, then others will start, resulting in a random "firing" of each alarm, so that they are not blasting in synch. Normally, it seems to "cascade" until they all blasting randomly, and this ramps up in stages, over a few seconds, like frogs peeping in a swamp. (My better half is a gourmet cook but lacks an externally-vented range hood, so this happens regularly).

Tonight, at random intervals of 15 min. to 90 min., they are going off. However, only ONCE tonight did one alarm "wake up" all six units, (in the "cascading" sequence I mention above) over several seconds, as in a valid smoke detection. Tonight, about 5 times a single alarm will sound one or two blasts, without triggers the rest. However, a couple of times, more than one unit was triggered, but not all six. Again, these single blasts are NOT the low battery chirp, which we are familiar with--rather, it is the first blast of a normal ramp up to full alarm.

Re: trigger sequence: Tonight, in a couple of the single or "two blast" incidents (i.e., not the full six-unit blast) we noticed that the offending unit was not the same each time. Once it was in the upstairs office yet another time it was somewhere downstairs.

None of the units are in the small, partial basement.

We've been through the whole house--no smoke smell. Occasionally, a distant woodstove in the area can be smelled in the yard--we shut the only open bedroom window, thinking this might be the cause (despite no smoke smell outside) but the alarms keep going off.

The wind is blowing heavily tonight, but not nearly as badly as last week, when we had no problems. Again, this just happened for the first time, tonight. We cannot tell if the wind is related to this.

The only thing I've done recently to the house, is to caulk up major air drafts in the basement "bilko" doors, a week ago. Our first thought was carbon monoxide, but the detectors (Model # 4120B) do not HAVE a CO detection function. We have nat. gas baseboard hotwater heat and a gas water heater, the latter being vented into the furnace's chimney. We have not used the fireplace in over a week, and we rarely use it at all.

We did have the stainless steel "rainhat" blow off of the brick chimney two months ago, and have not reinstalled it. As we have no CO function in the alarms, I guess this is irrelevant, but I mention it for greater minds than my own to consider.

THEORY: I understand (I think) that ionization smoke detectors work by sensing an interrupted stream of ions and electrons, when smoke particles attach to this stream emanating from the radiation source in the detector. Is it possible that wind is entering the chimney, forcing it's way past the closed chimney flue door, and disbursing ash particles from the fireplace, and triggering the alarms?

We've never known of a downdraft to come down our 2 story chimney, and when you hold a candle up to the closed flue door, there is always a moderate draw on the flame, but the door is fairly tight. The house is not dusty, and we see no ashes blowing around at all. HOWEVER, can old ashes cause a smoke alarm to go off? Just a thought....

A power blackout will not trigger the alarms, and our lights are not flickering at all.

If anyone has any idea what might be causing this, or things I can do to help narrow it down, I am all ears and WIDE AWAKE.

Thank you in advance!

Old 01-20-04, 06:25 PM
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Any particulate, including moisture condensing inside the unit can trigger a false alarm. This can happen if it's been damp during the day, and cold in the space at night.

The odd part here is that it's not latching into alarm. It's likely that the units may simply need to be cleaned (canned air works great for this).

The problem units may need to be replaced, however. Remember, the sensing element uses an unstable material that, while it should last most of a decade, sometimes poops out at 4 or five years.

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