New 'geofencing' apps offer deals and services but raise privacy concerns

Someone who is in a mall or near a favorite restaurant might get a message on their cell phone about a sale at a store or specials on the menu. Or they could be alerted that their child has left the school grounds. These are just a couple of the possible uses of a new generation of messages, apps and advertisements that go by the moniker geofencing.

McDonald's, Victoria's Secret and Best Buy all offer ways for potential customers to get messages on their smartphones about deals or specials at nearby locations. AT&T has been testing a free ShopAlerts service that sends location-based text messages about merchant offers. San Francisco-based Twitter is devising ways for merchants to deliver city-level advertising tweets to people based on their timeline. Foursquare lets people check in and receive ads and info linked to the areas where they are.

Emeryville-based Location Labs offers alerts and online reports about the whereabouts of family members, as well as services designed to prevent young motorists from texting while driving. Both of these are based on the mobile phone knowing where people are located or how fast they are traveling. Geofencing creates a digital perimeter around a location -- which could be a building, school or entire city -- that enables merchants or others to become aware when a person's cellphone crosses an electronic boundary.