Small round grille in headlining
 

Can anyone tell me what the small round grille in the headlining is, right above the driver's head? It's not a speaker - perhaps a sensor for the air-con? Just curious as to what it is.

'04 ZX71

Microphone for onstar or calling features?

Hmmm, that's strange then as there's a small black microphone stuck to the side of the front overhead console - I thought that was the OnStar mic?

As far as I'm aware there's no hands-free kit in the car (apart from the Parrot MK6000 that I've just fitted!)....

My 99 Blazer had both these fittings, it did once have a mobile phone hands free before I got it. I believe the round grille was for the speaker.
Adrian

Looks like I might have to remove the overhead unit at the front then - anyone know how it comes off?

Its a small fan that draws air in for the auto HVAC air temp sensor

So my original thoughts were correct - thanks for all the replies!