I have a piece of hardware that my grandma gave me along with her old laptop. I have no idea what it is and neither does anyone I know. It has a mono 3.5mm plug on one end, but plugging it into a headphone jack does nothing. Same result with a microphone jack. It has a 16 foot long cable. Pictures below.
Can someone please tell me what it is, what it does, and how to use it?
I used to have a TV card with a remote. The remote receiver was an IR diode in a casing, connected to the card via mini jack – just like the thing in question.
Notice the "REMOTE" label below:
The receiver itself:
Technically those things may send signals (like the other answer suggests) even if they were designed as receivers, I think. Still my bet is your mysterious item is a receiver shipped with some device and an IR remote.
Looks like an infrared sender. Old method of communication on some laptops, and external tools, though it depends on the frequency of light it puts out. That's all I can see it doing.
Normally the receivers are not clear, that is usually the sender. If it was a receiver it would be similar to the one in Kamil's answer, with a filtered input so that it doesn't confuse the incoming signals.
