But Banjo can sometimes reveal a user's location to people who don't know him or her. Users of Facebook and FourSquare whose information Banjo picks up may not be aware that they have enabled public sharing, for example. And while most Twitter users understand that their tweets are public, they are used to other people finding them by hashtag or username, not by their current location.

Jules Polonetsky, director of the Future of Privacy Forum, found that potentially troubling.

"I downloaded [Banjo], and it was great that I could see easily across my multiple social networks what my friends are doing and whether they're near me. But I also could see other people near me, and their pictures and information about them," he said.

"The idea that because I share my information, people I don't know can monitor whether I'm near them, is a bit disconcerting," he said.

But Polonetsky said he would go back to using Banjo because it was fun.