New in iOS 9 is a universal, contextual back button on the left side of the status bar. When you tap something in App A that takes you to App B, this back button appears as a fast, easy way to get back to what you were doing. Whether you use it or just leave it for a bit, it disappears.
When notifications attack
The interesting thing I’ve found is this behavior also kicks in if you tap a notification to switch between apps. This makes it especially handy to get back because App A didn’t send you to App B, App B’s notification did.
It’s worth noting this new behavior has some valid criticism. There isn’t much room in the status bar, so the back button covers both your mobile and wifi signal indicators. In some situations, you might switch apps to get something internet related, but nothing happens. Turns out your signal is weak, but you can’t check, and there’s no way to clear the button; you have to fall back to your homescreen or wait until it disappears.
[Update: Thanks to @rolphus, you can check your signal strengths fairly quickly by pulling down Notification Center. I haven’t had much time to test this, but it sounds like a good compromise.]
Maybe iOS 9’s new back button could cover the time instead of signal (hey, we all wear a watch now, right?), maybe it could be a single or multi-row colored band like the in-call and navigation banners. That’s for smart UI people to figure out.
Here’s the thing
As we switch between more and more apps to get things done, it became more obvious that we need a faster way to do the actual switching. The iOS app switcher has been ok and it’s still useful in a number of cases. But this new button answers that call to jump faster specifically between your two recent apps, or back to the actual thing you’re doing.
Of course, we can’t discuss this button without acknowledging Android has done something like this with hardware for a long time. But Android’s button is severely flawed and confusing because its behavior has never offered context or direction. Will I go back a webpage or switch apps? Will I switch apps or wipe out this note I’m writing?
In my time testing iOS 9, I think Apple’s approach is very well done. Excluding any possible UI tweaks, this button does a great job of appearing when you need it, and not wasting space when you don’t. Among the many other workflow improvements coming in iOS 9, it makes working in iOS refreshingly faster.