Having an off switch on a life saving device like that sounds like a profoundly bad idea to me, so not sure why it would be brought up in this context. I personally would’ve used an example of something you might actually want to turn off, but it would just be a bad idea, not a potentially fatal idea, if you failed to turn back on.
I was listing things where I would not want an off-switch along with the reasons. As you rightly mentioned yourself having an off-switch on a smoke detector is a very bad idea.
The only place where smoke detectors are frequently switched off are remote huts that might be empty for the better part of a year. And there the best strategy is to unmount the whole thing, pull the battery out and place both things somewhere really obvious so the next guys notice immediately what needs to be done.
Most firealarms I know have a button that switches of the activated sound when longpressed. I also do not know smoke detectors without removable battery (outside of wired ones).
A deactivation button is different from an power switch where the thing is off when the switch is in the wrong position. And if you don't notice people die. I didn't check the ISO norms on smoke detectors but I would be surprised if power switches wouldn't be explicitly forbidden in those norms.
And sure you can get a detector that doesn't conform to the norm, but then the insurance won't pay in case of a fire.
What an odd example to pick.