Know the real problem with elevator music? You never know who the DJ is. So when that really stellar track comes on midway through your penthouse ascent, there's no one to ask, "Is this Bacharach or Mancini?"

Instead you turn to Shazam, your new free iPhone app that has an ear for this sort of thing.

Just hold up your phone and let it listen for a second. Shazam compares the music to a database of nearly five million songs and before long—and with eerie precision—flashes everything you need to know: title, artist, maybe a YouTube video and, naturally, an upsell: the option to buy the song from iTunes.

The application is a lifesaver when you're driving and hear a new song on the radio that you want to add to your collection. But it really comes up big when trying to identify the most obscure gems.

Let's say you're watching Mad Men and Don Draper starts closing another (ahem) deal, the perfect period music purring in the background. Just hold your cell to the speaker and—viola—you've literally captured the mood: It's George McGregor & the Bronzettes' "Temptation Is Hard to Fight."

So why fight it?