2001 gmc yukon denali question?

[Jai]

To someone who owns this kind of truck: I would like to know what that speaker-looking thing above the driver's head is. Is it a speaker, a fan(??), OnStar-related part, or something else? We're clueless.
It is round, the size of maybe a half dollar or so, and it is above the driver's head.

 

[KenM]

i have the same thing in my sierra denali. it is a microphone for the on-star or if that early of denali had the phone than that as well.