Rolling / Earphones

Many people listen to music with earphones on the street. But earphone's cords are very long so the wires can get tangled easily.
There are many 'cord arranging product' in the shops but the products are big and heavy.Some people arrange the wire with a rubber band but that doesn't look good and can be inconvenient to rearrange.
And when people listen to music with earphones
they often put the MP3 in their bag or on a table and stand up,the earphones and MP3 player become seperated, sometimes forcefully.
These earphones have a magnet on the wire, so people can wind or unwind easily.
It's so simple.