“Have you noticed after 5 years the smoke detectors outside cover turn an ugly shade of brown? And it says “Do not paint” on them. LOL. I smell planned obsolescence.”
The reason for this (I’m pretty certain) is that bromine is used as a fire retardant in the plastic. Having the plastic melt instead of catching fire might give it another critical minute to keep blaring in a fire.
I should have read through all of the comments before making mine :-). You are right, it’s the bromine :-).