Answer by Vishnu Haridas:
This one I discovered recently: If you get an unusable headphones, don’t throw it away. You can cut & remove the wire, and use the TRS jack as the FM antenna for your smartphone.
All you need is to plug-in this TRS jack into your phone’s headphones plug, and open the FM radio app, then start listening through your loudspeaker.
How it works: The headphones wire works as the FM antenna for mobile phones. Usually FM transmission will have a very strong signal, which needs a small piece of wire to receive the signal.