Stuff you can't do

From Iphone

Things You Can't Do

The following is a list of features for which clients have asked that are either physically blocked by the OS or prohibited by Apple.

• Your sound-switch aware app cannot make noise when the screen is locked.

Reference: Link to developer.apple.com documentation

Relevant text: "Categories that obey the Ring/Silent switch do not allow audio when the screen is locked."

• Your app cannot "run in the background" while other apps are running.

In particular, you can't have your app, for example, monitor the GPS and buzz when the user gets close to their destination, unless your app is currently active on the device.