Replacing perfectly good smoke alarms?

Some, but not all, authorities and seemingly all smoke alarm manufacturers advise junking smoke alarms when they are 10 year old and replacing them with new ones. Is this really necessary? If so, with photoelectric detectors, ionization detectors, or both?

I’ve looked at the instructions for the two we carry, and it says nothing like that. Since they would be the ones to profit, it seems unlikely it’s a common recommendation.

They do ward about disposal though, because of the radioactive parts.

I believe the reason is that the ionization sensor decays with time. I also believe the alarms made today are substantially better than those made ten years ago. This is just stuff I’ve overheard on TV so don’t give it much weight.

The Ionizing sensor does decay over time. Father worked for the NRC, as the Public Affairs Officer at the time when these things really took off. There was a whole hue and cry over how safe it was to walk underneath a radioactive strip in the hallway outside your babie’s room ( It was always a baby…).

Here's the Straight Dope. You would stand on a stool so that your skull top was less than one foot from the smoke detector. You would stand there for one FULL year, nonstop. You would recieve less radiation than one day at the beach. ( And, don't give me that " A beach at the Equator or the North Pole" crap. We lived in Philly, Daddy was referring to Atlantic City no doubt ).

The risks are SO infinitessimal compared to the benefits, that they weren’t worth worrying about. Of course, people DID worry- hence Dad’s radio interview that I still have on cassette around here somewhere. In that, he did deliver the statistic given above.

One final and important thought. DO NOT THROW THEM OUT. If you are not sure if you have an Ionizing type or not ( or if you’re sure you do have one ), don’t throw it out with the garbage. One doesn’t want those strips to be incinerated. Call the local fire department and ask if they do disposal programs or if not, who in the area does.


The rule that we drill into the head of every elementary school student in the state is this:

  • Test the detector once a month.
  • Replace the batteries every 6 months (when you change the clocks back/forward).
  • Replace the detector every 10 years.

The battery is kind of a given, don’t wait until the detector goes “beep…beep…beep” every minute before you change the batteries, its easier just to change them at a reasonable time period. Quite often, when the detector gives the low battery alarm, the user will simply disconnect the battery and forget about it. A smoke detector without a battery is a just a lump of plastic on the ceiling.

Replacing the detector is a bit more complicated. As was previously mentioned, the sensing device, be it ionization or photoelectric, will wear out over time. Ionization detectors tend to lose sensitivity (they don’t alarm under fire conditions), and photoelectric detectors tend to gain sensitivity (greatly increasing false alarms, enough that people disable the detector). The solution the fire service has is to tell you just to replace the thing after 10 years.

I should add that this is only for what is called a “single station smoke detector,” the kind that has the sensing element and the alarm in the same unit…the one in most single and two family houses. If its a detector hooked to a fire alarm panel (apartments, commercial/industrial buildings), follow the manufacturer’s directions.

By the way, half-life of Americium-241 (the most common isotope used for smoke detectors) is 458 years, so the decay of the isotope is not the problem. I’d guess the sensors used to detect the current deteriorates first.