Debbie Young has a secret weapon in her quest for Black Friday’s best deals: her iPhone.

Using an app, or program, on her phone as a guide, the grandmother of seven from Counce, Tenn., plans to march into Toys “R” Us, Target and a few other retailers and grab just the gifts she needs on the day after Thanksgiving, the busiest shopping day of the year. The app—called TGI Black Friday—tracks deal flyers from top retailers, helping her map out her shopping trip.

“I don’t know how I would ever shop without my iPhone, especially this time of year,” says Ms. Young, 58 years old.

The battle for holiday shopping dollars is shifting to the palms of consumers’ hands. This year, there has been a surge in two kinds of shopping apps: price-comparison services and loyalty programs. The latest price-comparison apps keep track of sales flyers—online and on paper—giving shoppers unprecedented amounts of power. At the same time, retailers are pushing a new generation of apps that offer exclusive deals, coupons and loyalty perks to smartphone users who are near stores, in hopes of luring people in.

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