Every so often I find myself next to a car on the freeway with a driver that has earbuds in his ear. While the driver is jamming out to presumably whatever is on his iPhone, I often wonder what would happen if someone honked at him. Would he hear it?
The worst is when you see someone walking around with earbuds. Like a driver on a cell phone, the person walking is typically oblivious to their surroundings. They cross streets without looking, stop right in front of people on sidewalks, and will turn on a dime without any indication. People with earbuds are a hazard, particularly when they have the noise cannelling variety.
To combat this, essensy has created Awareness! The Headphone App. What Awareness! does is uses the iPhone's internal microphone to pump sound to you while you are listening to your tunes. For example, if a train is coming, blaring its horn to warn you of its impending arrival, Awareness! will pump the trains sound from the microphone into your earbuds.
The app is pretty new, and I'm sure it needs some tweaks to be perfect, but it is getting a good amount of iTunes love. There are a few bad reviews, but the majority are five star reviews that say things like, "What an awesome app!!!!" and "I love it, LOVE IT".
If you often find yourself in harms way due to your high end Shure headphones, I implore you to give Awareness a try. For the sake of humanity, just do it.