According to Eater, you can score a free ShackShack burger using the iOS (sorry Android folks) app. Just use code shackappy to checkout.
How to get free burger:
- Visit the companies website by clicking “Get This Offer (External Website)”
- Install the app, create an order with a single ShakeBurger (up to $5.55 in value) and then use code shackappy to checkout to make it $0.00.
- Head to a local Shake Shack location to get it!
* One burger per user. iOS device required. Offer expires on Tuesday, February 28th, 2017.