Did someone steal the americium?
September 25, 2011 11:40 AM   Subscribe

Why did my two smoke alarms stop working altogether when the batteries ran down?

I have two smoke alarms which I installed on the same day, two years ago. One is in the downstairs hallway, one is at the top of the stairs. They are both the round white 9V PP3 battery powered ionisation type. I changed both batteries a year ago when the alarms started to do the beeping thing that indicates low battery power. I test both alarms regularly, and the one downstairs does occasionally go off if I overcook the bacon. So I know they've worked fine all this time.

Last week, one of my two smoke alarms started to do the battery beep again. I put in a new alkaline battery. The alarm didn't work. I tried another battery from a different batch. Still no luck. The alarm appears to be dead.

Then, today, the second alarm started to beep. I replaced the battery. Again, the alarm didn't work. So that alarm also appears to be dead in a manner identical to the first.

So what happened? Is this just coincidence, or is there some mechanism (inbuilt expiry or something) that would cause this apparently identical failure after a nearly identical time?
posted by le morte de bea arthur to Technology (7 answers total)
I've had this happen. It was explained away by "obsolescence," which is not good enough.

I installed a bunch of alarms which came supplied with a 10-year battery. I test them every week and they are still in working order after 4 years. It helps to vacuum them once a week, though I can't say I've done this myself.
posted by tel3path at 11:48 AM on September 25, 2011

Cheap batteries? Leaking and corroding the points?
posted by MuffinMan at 11:54 AM on September 25, 2011

Is there an expiry date on the alarms? Maybe on the underside? Two years seems like a short time. This happens with carbon monoxide detectors, but is typically 5yrs from day of manufacture and is a feature not a bug.
posted by dismitree at 12:04 PM on September 25, 2011

Smoke Detectors have a surprisingly high failure rate. By some estimates, they fail 40% of the time within the first 5 years. This is especially true of the cheaper photo only alarms that they sell at the big box stores.

Smoke detectors that are hard-wired, inter-connected, with battery back-up, and that are both ion, photo, and carbon at the best - but even the good ones fail.

NFPA section 72 (a building code adopted in most of the US) requires that all smoke detectors (even the high end ones) be replaced every 10 years. (Though, almost no one enforces or follows this particular building code. The smoke detectors in your local library, for example, are probably 25 years old, and have not been tested in years.)

Whether you have expensive ones or cheap ones, you need to test them often, and be prepared to replace them regularly.
posted by Flood at 12:08 PM on September 25, 2011 [1 favorite]

9V batteries are sometimes difficult to insert. Make sure the polarity is correct, and press until the contacts are fully locked.
posted by weapons-grade pandemonium at 12:11 PM on September 25, 2011

Well, the Americium has a half-life of 432.2 years, so it hasn't decayed away.

It emits about a 6 Mev alpha particle, which means that the recoil is pretty huge, more than enough to rip the atom out of any lattice and produce a lot of very local heating, I'd think.

Maybe the Americium vaporized itself away.
posted by jamjam at 1:19 PM on September 25, 2011

Looks like it's 'just one of those things'. Definitely wasn't the battery connections - they were those snap-on battery clips attached to wires and there was no sign of corrosion or leakage.

Anyway, thanks for the suggestions.
posted by le morte de bea arthur at 3:06 AM on September 30, 2011

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