What's causing my smoke alarm to go off???

Home Inspector with Schuerman Inspections, LLC.

Recently I received a request for information (RFI) from a past client who was experiencing a problem with her smoke alarms going off without a smoke incident. Here is the email:

Hi Dan,

I have a question you may be able to answer for me. This morning my smoke detector went off a few times—just some quick shrills—not a continuous ring. It was the most horrific sound! Thankfully there wasn’t any smoke and I was trying to determine if there was a problem with the detector. I got up on a ladder and looked at the detector (did I even know what to look for?) I’m thinking about asking the fire department next door to come over and check them for me. Do you know if the detectors have a tendency to just go off (usually if the battery is low they would chirp, although I’ve never had these kind before that don’t require changing the battery). I do remember when you were doing the inspection that you were talking about the detectors (although I confess, I don’t remember everything you said).




I followed up with her with this response and felt it was worth posting for every ones benefit:


There are several things that can trigger your AC powered smoke alarm when no smoke is present. Any of the following situations can cause unwanted alarms: (although the most common is dust in the sensor chamber)

1) Cover or sensor chamber is covered by dust or dirt. Alarms may look clean, but dust, dirt or insects can accumulate inside the cover. Gently vacuum smoke alarms regularly using the soft brush attachment.

2) A loose electrical connection on at smoke alarms may be the cause. In AC or AC/DC smoke alarms, a loose hot wire connection can intermittently disconnect power to the smoke alarm. The effect is the same as a power failure. When power resumes, the units can alarm for a short time. Also, a loose or disconnected ground wire may cause the alarm to chirp or go into alarm. Be sure the alarm has been properly connected.

3) Sometimes power interruptions to AC smoke alarms can be the cause. Smoke alarms may alarm for a short time when power is interrupted, then restored. Power interruptions are common in areas where utility companies switch grids (usually in the early hours of the morning).

4) Alarm was triggered from another part of the home. Most newer homes constructed within the past 15-20 years are daisy chained (interconnected) AC or AC/DC alarms. Sometimes, the unit triggering the alarm is in another part of the home and it is causing other alarms to signal.

Some other circumstances that may also cause this problem include:

Smoke from the initial stat-up of a furnace due to dust burning off or drywall dust in a new construction home entering the monitor. Humidity in ionization smoke alarms may also trigger nuisance alarms when they are installed near a bathroom as are smoke alarms placed near a cold air return because dusty air can be blown through the alarm sensing chamber.

A good rule of thumb for placement of detectors is to place them at least 20 feet from appliances like furnaces and ovens, at least 10 feet from high humidity areas like showers and laundry rooms, and at least 3 feet from heating and air conditioning vents or fluorescent lights wherever possible.

I have had ours go off numerous times since we built our home in 1997 and we replaced them this year. (Fire marshals and manufacturers recommend replacement every 10 years). Newer units do have back up batteries that will chirp if the batteries get low. The best rule is to replace the batteries every 6 months to 1 year max.

Hope this helps!

Dan Schuerman

Schuerman Inspections


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