By shelf life I mean usage life.
This morning, 4am (it's always 4am for the random ones!) the two mains powered smoke alarms in the house go berserk. I think they are linked, in any case? Not sure of model, or whether thy have battery backup. They were in the house when we moved in 8 years ago. Don't recall having a problem with them before.
They eventually went off, then on again 5 mins later, then off. Not struck up since. No sign of fire, smoke, heat, inside or out. Not particularly dusty, smoky or hot in the house.
So, assume it's a spurious alert, are they on their way out and should they be replaced?