While some people may not care, for others it is a habit to make sure the left ear phone is in the left ear and right earphone in the right ear. For some audio sources, it won’t matter much, but others, like movies and video games, require the proper channels are going to the proper ear. (You don’t want to turn the wrong direction when an alien, orc, or other enemy is firing at you.)
To solve this problem, researchers at the Igarashi Design Interfaces Project have added electrodes to the front of ear buds. When the buds are put in the correct ears, the electrodes will be against the outer ear, which will form a connection. If the ear buds are reversed though, the electrodes are out in the air and not making a connection. This then triggers a chip to switch the channels, thereby ensuring the proper audio is going to its proper place.
The researchers went a step further with this though, as they also added a way for the earphones to know when they are being shared by two people. When worn by one person, there will be a weak electric current between the ear buds, but when two people wear them, the circuit is broken. This causes the chip to combine the stereo channels into a mono channel, which is sent to both ear pieces. This way both listeners get all of the audio.