Gas station without pumps

2016 August 30

Smoke detector to avoid

Filed under: Uncategorized — gasstationwithoutpumps @ 21:16
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When I was getting the solar panels installed last year, the Planning Department insisted on us installing new smoke+CO detectors, replacing our current smoke detectors.  I was not real thrilled with the idea, but I let the contractor install the new detectors to keep the building inspector happy.

I was under the impression that CO detectors should be installed low (unlike smoke detectors, which should be installed high), but that turns out to be a myth—CO diffuses rapidly through air and can be equally well detected either high or low.  CO has a molecular weight of 28 g/mol, compared to 29 g/mol for the mixture of gases in air, so if it did stratify, it would be high, not low. The main constraints of CO detectors is to keep them out of bathrooms (too humid) and at least 15 feet from stoves (small amounts of CO emitted during cooking—need to dilute it to avoid false alarms).

The detectors that the contractor bought were First Alert Model PC910, a smoke+CO detector with a 10-year battery. This post is a review of our experience with the smoke detectors over the past year.

Here is the front of the First Alert PC901 smoke detector, with the cover pried off and not fully replaced.

Here is the front of the First Alert PC901 smoke detector, with the cover pried off and not fully replaced.

At first the alarms seemed fine—pressing the test button gave an easily audible alarm, and the detectors looked no worse than any other smoke detector. But a couple of weeks after installation, the alarm woke us up out of a sound sleep. Detecting no smoke in the house, we pressed the test/silence button—no effect. So, desperate to shut the thing off, we took it down and tried to deactivate it.

There is an "off-switch" on the back, but to use it, you have to break off a tab (only possible with tools) and permanently disable the device.

There is an “off-switch” on the back, but to use it, you have to break off a tab (only possible with tools) and permanently disable the device.

It is rather annoying that the first false alarm from the device disables the $50 device permanently—seems like a scam to me.

A week later the second smoke alarm did the same thing, but this time I was able to pry the lid of and turn off alarm by disconnecting the battery without necessarily permanently deactivating it. I reconnected the battery the next morning and everything seemed fine, until it gave another false alarm in the middle of the night two days later.  I disconnected the battery again and left it off.

I figured I was done, but about a year later (earlier this week), the last of the smoke detectors gave its false alarm and couldn’t be turned off—I had to pry the case open and disconnect the battery.

The wires from the blue battery have been disconnected from the white header on the PC board. The big brown cylinder is the CO detector, the white disk on the bottom left is the loudspeaker, and the black box in the middle is where the LED and photodetector are housed for the optical smoke detection.

The wires from the blue battery have been disconnected from the white header on the PC board. The big brown cylinder is the CO detector, the white disk on the bottom left is the loudspeaker, and the black box in the middle is where the LED and photodetector are housed for the optical smoke detection.

All the false alarms were from the smoke detector, probably as a result of dust or cat hair confusing photoelectric detector. I expect a certain number of false alarms from smoke detectors, particularly resulting from kitchen activity, but getting false alarms in the middle of the night with nothing obvious triggering them is super annoying (I never had that sort of false alarm from my old smoke detectors).

What irks me most about the First Alert detector is that I was not able to turn the alarm off after a false alarm—the well-hidden “silence” button simply didn’t do anything. The design of the smoke detector so that you need to destroy the device to turn off a false alarm is absolutely unacceptable design. I will not buy another smoke detector from First Alert.

The Planning Department’s insistence on smoke+CO detectors has backfired—we’ve gone from having working smoke detectors (but no CO detectors) to having no functional detectors (except in the book room, where the older, unreplaced smoke detector is still working).  I’m out about $150 (plus installation costs) and have to go out and buy new smoke alarms, so it will cost me a total of over $200 to get back to the level I was at before the ill-advised purchase of the First Alert devices.

I’m currently considering Kidde i9010 ionization smoke alarms with 10-year batteries (the ionization devices are less subject to false alarms from dust than the photoelectric ones) for the bedrooms, and a Universal Security Instruments MI3050SB alarm with both ionization and photoelectric sensors for the dining room, where false alarms will be less annoying.  I’ll probably get a couple of plug-into-outlet CO detectors as well, probably Kidde KN-COPP-3 CO detectors, because I like that they display the CO concentration.  It is cheaper to get combined smoke/CO detectors, but I they all seem to be photoelectric, not ionization detectors, and I’m now leery of photoelectric smoke detectors in the bedroom—dust/cat-hair false alarms are too irritating.

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