Telling Friends Where You Are (or Not)

Mobile services like Loopt and Google's Latitude have promoted the notion of constantly beaming your location to a map that is visible to a network of friends — an idea that is not for everybody. But now there is a different approach, one that is being popularized by Foursquare. After firing up the Foursquare application on their phones, users see a list of nearby bars, restaurants and other places, select their location and "check in," sending an alert to friends using the service. This model, which may be more attractive than tracking because it gives people more choice in revealing their locations, is gathering speed in the Internet industry. Yelp, the popular site that compiles reviews of restaurants and other businesses, recently added a check-in feature to its cellphone application. And Facebook is expected to take a similar approach when it introduces location features to its 400 million users in coming months. If checking in goes mainstream, it could give a lift to mobile advertising, which is now just a tiny percentage of overall spending on online ads.