What are these for?
 

I have a 2000Blazer 4dr with the "Trail Blazer" package. I would like to know what 2 things are. 1is the sensor in the middle of the dash defroster that looks like the light sensor in the right front dash speaker grill. 2nd is the thing that looks like a small speaker grill in the headliner above driver side window. Thanks for any info.

The sensor on the dash is a light sensor for your automatic lights.

And I believe the speaker grille is where the microphone is if you have OnStar.(the grille is still there even if you don't)

Thanks chevyriders for the info on the onstar part. I have another one of the I am guessing it is a light sensor but it is in the middle of the defrost vent in the dash wasn't sure what it is for. My neighbor has an Equinox, newer than my Blazer but that thing blinks red when they have car locked up, just curious about mine.

The 50 cent sized grill thing in the headliner is actually part of the HVAC system. There is a little fan in there that monitors this that or something...

Thanks CWBDDSPC, that's exactly what it looks like. Still haven't figured out the sensor in the middle of the defroster vent on top of dash.

Checked with a chevy dealer in Ft. Wayne and was told the sensor in the middle of defroster vent in dash is a sun load temp sensor for the auto hvac system.