Carry Alerts is a new iPhone app that runs in the background and will alert you when you are near a local, state or federal gun free zone as well as reminding you to do what you need to do when you get close to an international border. The app is designed with conceal carry holders in mind who want to avoid inadvertently breaking the law.
Most of us are on Android so we could not test this app, nor was the TFB party yacht available to see if it could alert us when we reached international waters. The app is selling for $2.99, which I think is reasonable. I would actually rather it was a subscription based service, maybe $2 / year, so that the author had an ongoing incentive to keep the database up to date.