said by TheMG:Sorry if this is a little OT, but this got me thinking...
I've got no idea of the age of the smoke detector in my apartment, but it does beep when press the test button.
However, how can one be sure that it actually detects smoke and that the radioactive material isn't completely decayed?
If the detector is truly an ionizing detector, the effective life is 10 years. It's a function of the half-life of the alpha emitter (typically Americium 241). Once enough of the material is gone,it is no longer effective.
Those sensitive to heat rise, or are photoelectric can last longer. I don't have any numbers on these however.
All three detection modes have their pros and cons. Some of the better ones are multi-mode (e.g. photoelectric and ionizing).
If you don't know when they were put in, you can usually check in the case for the date of manufacture. If that's not available, best change it.