Randomly meeting a friend in the street may soon become a thing of the past -- social media will have told you they're coming. Today Facebook has introduced a new "nearby friends" feature that lets users know automatically if their friends are in the vicinity. The feature is optional, but if you turn it on, you'll occasionally be notified when friends are nearby, so you can get in touch with them. (For example, if you're headed to the movies, Nearby Friends will let you know if friends are nearby so you can see the movie together or meet up afterward.) You can also restrict who can see if you're nearby -- for example: your friends, close friends, or a specific friends list -- and you can choose to share a precise location with the particular friends you choose for a set period of time. When you share your precise location, the friend you choose will see exactly where you are on a map, but they won't be able to track where you are all day.