Facebook Can Now Track Your Precise Location Continuously Through Your Phone (FB)

Today, Facebook launches a new function for its Android and iPhone apps called "Nearby Friends", which allows users to track each others' locations continuously down to the nearest half mile or — if you choose — as near to your precise location as possible.

Yes, it's optional. By default the new feature is turned off. You must choose to activate it.

Once you've got Nearby Friends turned on, however, you'll be able to see the location of any other friends who are also using Nearby Friends at the same time. And they'll be able to see you. The system uses GPS and triangulation between cellphone towers to get your location (the combo reduces the drain on your battery that would be pronounced with GPS alone). It then produces a map with all your friends on it.

Facebook believes it will be most useful for people trying to find each other in airports, shopping malls and parks — places where it's often difficult to navigate because they're huge and have no street addresses. You can use the map to walk directly toward them.

To prevent stalking, the function comes with a timer that switches off Nearby Friends after a certain time, for instance one hour. And only friends can see you in Nearby Friends — not friends of friends or members of the public you have not confirmed as friends.

Nearby Friends also produces an activity log, which you can delete at will. The log also produces maps of your whereabouts over time, which you can also delete if you want. Here's someone's trip from Brooklyn to JFK airport and then to Manhattan (below). You can tell by the dot spacing how fast various parts of the journey were:

Obviously, the new feature has the potential to produce a lot of new data on users. Facebook product manager Andrea Vaccari says that, currently, none of that data will be used for purposes outside the app. It will not be used to help target advertising, for instance. And Nearby Friends will not be usable by business Pages that you're fans of — so local restaurants and stores won't be pinging you with offers when you walk by. (Of course, given Facebook's track record, it would seem natural that such a useful new trove of location data might eventually be monetized in some way in the future.)

In short, the fact that it's voluntary, opt-in, and limited only to people who you want to see you will seriously restrict its use as an app for stalkers — a variable that Vaccari is painfully aware of.

Vaccari came to Facebook when his startup Glancee was acquired by the social network. In 2012, he told Business Insider, Glancee was just an app that allowed Facebook friends to track you in real time, and vice versa. It was a hit at SXSW. But Glancee was running out of money, and Vaccari was so pressed for cash that he was sleeping in a closet in San Francisco rather than an apartment, to make ends meet.

But a series of meetings with former Facebook product manager Josh Williams and former product director Peter Deng led, ultimately, to a meeting with CEO Mark Zuckerberg himself at the Menlo Park HQ. "I woke up in a closet and went to meet Mark Zuckerberg!" Vaccari says. "We realized it would be a lot more powerful to build it as part of Facebook" than as a standalone app. The terms of the deal were undisclosed — but Vaccari became a Facebook employee and has been working on the Friends Nearby ever since.

About 5,000 Facebook employees have been testing Nearby Friends prior to today's launch.

Here's what the new function looks like.

Nearby Friends only works if you choose to switch it on:

Once it's on, it shows you the location of any of your friends also using the function.

Nearby Friends tells you the location of friends within a half-mile radius of where they are. If you want more info, you can share precise location data with individual friends.

Here's Facebook's official description of the feature:

Sharing your location with Nearby Friends goes two ways -­‐-­‐ you and your friends both have to turn on Nearby Friends and choose to share with each other to see when you're nearby. Your friends will only be able to see that you're nearby if you share this info with them and vice versa.

And here's a video of the thing in action: