Loopt Star is Loopt’s effort to play catch-up with some of these other services, particularly with Foursquare. Loopt, which started in 2005, was one of the first companies to popularize broadcasting one’s whereabouts to friends. But Foursquare, founded last year, is a popular newcomer. It turned location-sharing into a game with its badges, mayorships and rewards, and into a marketing tool for businesses, including Tasti D-lite and Pepsi, to track and reward loyal customers.

Loopt has 3.4 million registered users to Foursquare’s 1.4 million users. But Foursquare’s gaming elements are quickly attracting new users. Mr. Altman said Loopt built Loopt Star in response, and last year acquired a start-up called GraffitiGeo that builds similar games.

Image Checking locations of places to shop for possible reward points on the Loopt Star mobile game. Credit... Peter DaSilva for The New York Times

“We respectfully just sort of knocked off those gaming elements, but added new things,” he said.

People register for Loopt Star using their Facebook log-ins, so they can share their location and compete in the game with their Facebook friends and alert their friends about recent purchases and special deals.

Retailers can choose which actions they want to reward and what the prizes will be. Gap is sending customers a 25 percent discount coupon after they check in twice to a Gap store. Burger King is offering a soda with a sandwich or a coffee with a breakfast sandwich to people who check in three times. Universal Music will send five free songs to people who check into any bar along with two friends.

Stanford University is using Loopt Star over graduation weekend. When students check in to at least two of the official school events, they will get a prize. Once they have left Stanford, they will be able to use Loopt to find fellow alumni, said Ian Hsu, Stanford’s director of Internet media outreach.

Starbucks will use Loopt Star to give frequent customers an honorary barista badge, symbolized by a green apron. Starbucks also offers a barista badge on Foursquare, where people compete to become “mayors” of places, and the coffee chain is giving mayors $1 off Frappuccinos.