[tialaramex]

Fixed lifetime suggests ionization rather than optical sensor? If so yeah, they have a specific lifetime, it's just physics. There's an Americium-241 source, a tiny, tiny amount of radioctive material in a sensor which is decaying constantly, and once it has decayed a certain amount too bad, buy a new smoke detector.

There are arguments for or against both types, but ultimately "Make sure you replace it every ten years" doesn't feel like a huge problem. If you really can't do that, then the optical sensors don't have this property - they will still need new batteries, but of course you can just swap those out on a schedule when it suits you, they're typically a cheap household 9volt battery (yes even for a mains smoke alarm, fires don't magically stop when the power goes out)

[cowsandmilk]

> Fixed lifetime suggests ionization rather than optical sensor?

Not at all. The 10 year lifetime is something that was set by people concerned by the lifetime of the electronics. The half life of the isotope in smoke detectors allow them to last well beyond 10 years. (The half life is 432.2 years)

[tialaramex]

I was aware that the half-life was much longer but I'd assumed the 10 years was based on the fact that nevertheless we're talking a degraded sensor performance over time, however it does seem like it's actually 10 years because they're worried the electronics will crap out, so you're right.

[sidewndr46]

I installed some gas sensors like this a while back. It says in the manual that some date after installation they trigger and stay that way permanently.

[oniony]

No, but you'd think they could charge a battery/capacitor during the good times and use that charge during the outage.