A known way to turn off in iPhone if the screen isn't detecting touch is to let go of the home and power buttons as soon as the screen goes black. But this sometimes doesn't work, and instead the iPhone restarts. I wonder why.
Well, the iPhone restarts because pressing the Home and Power buttons simultaneously for a longer period is actually the way to force a restart (on the iPhone 6S and earlier). I think you're simply holding them too long.
I found two ways to do it:
- Force restart and press home to put the iPhone in recovery mode (it will show a cable icon of sorts).
Once in recovery mode, unplug the iPhone. It'll turn off in less than 1 minute.
- Hold the Home and Power buttons (just as you do to reset the iPhone), until the apple logo appears and then disappears, the iPhone is turned off. It takes around 14 seconds in my iPhone 6.
- Another more traumatic one is to open the iPhone, and disconnect and connect the battery connector. It won't turn on again.
This ways to turn off an iPhone are working for me while using iOS 10.3.2. Not sure if in future updates this ways will work.