Eli5: what are those big shiny domes on the ceilings in public places

Question

I see them all the time and have no idea what they’re for

In: Engineering

Answer 1

The mirrors that stores often have so that clerks can see down aisles and around corners from the till to keep an eye out for shoplifters? That is about the only thing I can think of that matches the short description you have given. It is tech heavily utilized before the implementation of security cameras, and one that is still commonly used as they are cheaper than cameras and computers.