Are you one of those people who’s crossing the street, completely oblivious to everything around you, because you’re plugged into your headphones?
Yeah, us too.
Basically, it’s a little sound mixer that you plug in between your ear buds and your iPod, smartphone, mp3 player, whatever. It has a powerful microphone on it, so it can pick up ambient sound. It pipes that through your ear buds along with your music, and bam—you get your music and aren’t wondering around like a zombie.
Helpfully, you can adjust the sound levels of that mic, so you could turn it far down and only be alerted for fire alarms and car crashes, or turn it way up and listen to music at your desk at work while retaining the ability to react to the nonsensical ramblings of your coworkers. You could even leave your ear buds in and have a conversation with someone, but you shouldn’t do that, because that would make you a dick.