Friend Stacker App Works by proximity. Each participant chooses one ingredient and, when they stack their smart phones, the phones recognize each other to build the hamburger. Then, the app rewards them with a coupon. The app replicated its activity on Facebook and was introduced to the most loyal consumers through BK’s fan page and through QR direct download codes inside BK restaurants.

The total amount of free hamburgers set apart for this promotion lasted less than a week. Sales of the paid stackers increased 17% during the implementation month.