Holla,
Welcome to the forum.
Crow pir's were bloody brilliant, used to use them in 'Harsh' enviroments and never had any problems at all.
Hated DSC panels though. Customers just couldnt even tell you what the problems were coz the display clears after a few seconds, lol..
I have seen them last 15+ years with no issues. I am torn tbh, if maintained regulary with no issues i am not sure i would replace them.
Unless comoany policy us to recomend replacement of course
If they are working and you are not bothered that they look yellow no real reason to replace imo.
But if any signs of false alarms/issues rip them all out and replace with shines new ones.
I know many company's that would make you "Recommend" replacing PIR's after 10 years. You decide if it's the company generating extra revenue or looking after the customers needs ..