Apple's polished iPhone lineup comes with tools to help users dial back their smartphone obsessions, amid growing concerns over "addiction" and harmful effects on children.

An iOS 12 mobile operating system that will power new iPhones unveiled on Wednesday, and be pushed out as an update to prior models, has new features to reduce how much they distract people from the real world.

Apple senior vice president of software engineering Craig Federighi said of iOS 12 at a developers conference earlier this year the new system offers "detailed information and tools" to help users and parents keep tabs on device use.

A new "Screen Time" tool generates activity reports showing how often people pick up their iPhones or iPads, how long they spend in apps or at websites, and numbers of notifications received.

Users will be able to set limits on time spent in apps. Parents will be able to get activity reports from their children's iPhones or iPads, and impose time limits on apps from games and news to social media and messaging.

The operating system will also allow people to designate "down time" when iPhones or iPads can't be used -- perhaps a child's bedtime or a grown-up's meditation hour.

Activist investor Jana Partners and the California State Teachers' Retirement System (CalSTRS), which both have stakes in Apple, early this year called on the company to give parents more tools to ensure children are using its devices in ways that aren't hurting them.

The investors reasoned that doing so would pose no threat to Apple, because the company makes the bulk of its money selling devices, not from how much people use them.

Apple has been working to ramp up revenue from services and digital content such as music and movies, but most of the cash it takes in comes from iPhone sales.

The letter cited a growing body of evidence that excessive smartphone use may be having negative consequences on young people.

A study of teachers found the vast majority felt smartphones were a growing distraction at schools, eroding the ability of students to focus in class and a seeming cause of social and emotional difficulties.