This app was so popular when it first came out that the developer had to pull it due to server overload and a issue with glitches.
It's back, and available for free.
Yes, it's a little slow right now and doesn't have every product, but with user input, I think most products will be on there rather quickly. I scanned some stuff that I have in my house and of course, found that there are GMOs in them, related to Monsanto.
You can choose what campaigns you want to support, and the app will tell you if the parent company goes against your principles.
http://www.buycott.com/
https://itunes.apple.com/us/app/buycott/id585933440?ls=1&mt=8
https://play.google.com/store/apps/details?id=com.buycott.android
http://www.forbes.com/sites/clareoconnor/2013/05/14/new-app-lets-you-boycott-koch-brothers-monsanto-and-more-by-scanning-your-shopping-cart/