Burger King: How do you order a Whopper sandwich for a penny at McDonald’s?

No, it’s not the start to a really bad joke.

It’s called a ‘Whopper Detour’ is what it is. The burger chain is smartly pushing people to download its app (or use it, if they are among the millions who already have it) by offering a one-cent Whopper.

The catch: Patrons have to place the order on the app while they’re inside or nearby a McDonald’s. The app will then direct them to the nearest Burger King to redeem the offer.

https://www.youtube.com/watch?v=Pg5EmtaSCL4

The app uses geofencing to determine if the customer qualifies for the promotion. If you’re within 600 feet of a McDonald’s location, the burger is yours for a fraction of its usual price. Once the order is placed, the app will lead customers to the closest Burger King. The promotion begins Tuesday and will end December 12.

Burger King stated that FCB New York approached it with the premise about a year ago. “We love ideas that when the idea gets to us we say ‘how the heck are we going to pull this off?'” said Marcelo Pascoa, BK’s global head of brand marketing.

The “Whopper Detour” campaign took a bit of tech savvy to pull off. In order to implement, they had to geofence nearly every McDonald’s restaurant in the U.S., as the offer only unlocks within about 600 feet of a McDonald’s.