NEW YORK - Walgreens has launched a mobile marketing tool from LocalResponse that sends instantaneous offers to customers who enter any of its stores and check-in via mobile apps such as foursquare or Yelp, Advertising Age reports.

For example, when a customer checks in via a mobile app and tweets, "I??m here" via Twitter, Walgreens might send a message back: "Check out Halls new cough drops in the cold aisle." Walgreens sent out 5,000 Halls messages alone last month via Twitter.

Walgreens has also been testing less direct mobile marketing strategies. For instance, when visitors checked in to a drugstore via a foursquare or Facebook mobile app, the retailer donated free flu shots to charity on their behalf. For Energizer, Foursquare check-ins launched a mobile coupon for a four-pack of batteries.

The strategy has been effective: According to Adam Kmiec, Walgreens?? director of social media, the Energizer promotion generated stronger redemption rates than traditional digital coupons.

LocalResponse President-Founding partner Kathy Leake said Walgreens is the first retailer to publish deals for packaged goods via its tool.

For more on mobile loyalty marketing, see "The Strength of Mobile Loyalty Marketing" in the February NACS Magazine.