Backtap on iPhone is a cool feature for everyone, but it started as an accessibility feature. When you enable back tap, actions can be triggered by double and triple tapping the back of the phone. For example, if you don't want to fumble around to find the flashlight on the screen, you can enable Flashlight as a double tap on the back of the phone to turn it on and off.
Watch Apple's video, How to use Back Tap on iPhone (YouTube 1:01 min) for quick instructions and give it a try!
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