My wife and I just bought a new to us home in Georgia.
The home was built in the 1980s and has rigid duct work going from the air handler to the ducts on the first floor. There may be some flex in there somewhere to make it quieter a bit, but I'm not 100% about that.
What I do know is that some vents have a two conductor wire running to them. Its brown, twisted upon itself, currently has no voltage to it, and appears to be low voltage in nature. I know that HVAC typically runs at 24VAC, so my working theory is it went to something like that.
My question is what could it be? Its not running IN the ducts, just zip tied to the outside of them the whole length.