Retailers have long turned to circulars and signage to tell customers what packaged goods are in-store. In recent weeks at Walgreens, the mobile check-in has been following suit.

Using a tool from startup LocalResponse, Walgreens finds public check-ins at its stores and sends users reply messages via Twitter. For example, when customers check in to any of the chain's 8,000 stores through mobile apps such as Foursquare or Yelp and publish "I'm here!" to Twitter, Walgreens messages back: "Check out Halls new cough drops in the cold aisle."

Walgreens has a long-standing relationship with cough-suppressant Halls for promotions in stores and on its website. In the effort, Walgreens sent out 5,000 Halls messages in January via Twitter.

Walgreens has also been testing other means to use social media to make customers aware of products. When visitors checked in to the drugstore via a Foursquare or Facebook mobile app, it donated free flu shots to charity on their behalf. For Energizer, Foursquare check-ins served up a mobile coupon for a four-pack of batteries. The Energizer effort saw better redemption rates than traditional digital coupons, said Adam Kmiec, Walgreens' director of social media.

Walgreens is the first retailer to use LocalResponse to publish deals or promotions for packaged goods, said President-Founding Partner Kathy Leake. It will be the only drugstore chain to use this feature for at least one year.

LocalResponse raised $5 million in venture funding last fall, led by Vodafone Ventures and Cava Capital.