Electronic – Smoke detectors replacing – why? Lifetime of components

lifetimesmoke-sensor

I often see that smoke detectors "should be replaced" every 5, 10 or 20 years. Like on this website for example: http://modernsurvivalblog.com/health/did-you-know-smoke-detectors-expire/

The U.S. Fire Administration says most smoke detectors installed today have a life span of about 8-10 years. After this time, the entire unit should be replaced.

I wonder why? It probably has nothing to do with half-life of Americium 241(because it is 432 years), so what is the reason? I though about electrolytic caps, but mine for example has only one and its lifespan is often much higher than 10 years(if it is not piece of crap). I don't see any other electronic-related problems with the circuit in this things, it is pretty easy and hardly anything can break inside if it just sits on the ceiling doing nothing 99% of the time.
Is there logical reason or is it "just in case"?

Best Answer

As you suspected, apparently it has nothing to do with the radioactive material in those alarms that use it.

According to the Reliability section for smoke detectors:

The NFPA strongly recommends the replacement of home smoke alarms every 10 years. Smoke alarms become less reliable with time, primarily due to aging of their electronic components, making them susceptible to nuisance false alarms. In ionization type alarms, decay of the 241Am radioactive source is a negligible factor, as its half-life is far greater than the expected useful life of the alarm unit.

So it is just a matter of component reliability. Although we are used to some electronic devices working for decades, we also accept that sometimes (but very infrequently) they just up and die, and perhaps on a statistical basis 10 years has been found to be a good marker for these alarms where one can be assured some large number of units (99% or higher?) will still be working.

Anecdotally, the house we are currently living in was built 20 years ago. We bought it 10 years ago. It has 10 smoke alarms in it. I never knew about the "replace every 10 years" rule. About two months ago, some of the alarms started to go off on their own (false alarms). After this happened a couple of times, I replaced them all.

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