At one end of the wire is a 3.5 mm Jack plug. On the other end of the wire is presumably a glass LED.
When connected to the phone, nothing happens. The LED does not start to glow.
Also, this wire doesn’t work as a microphone. It’s also not an earpiece.
What is it for?
Yep. Used to record all sorts of TV shows on my computer using them. Though they aren’t nearly as prevalent since Internet streaming has taken over. I doubt I could pick up more than 2 or 3 channels over-the-air where I live anymore.