My iPhone 6 switched off on me a few times, and so far it has happened once to my 6S.
However, whereas the 6 would restart again as soon as I pressed the power button, the incident with the 6S this week was different.
Firstly, it wouldn't power back up again when I pressed the power button.
Secondly, my Apple Watch didn't show that it had lost contact with the phone, and the watch apps continued to function normally, which they cannot do unless the phone is on.
Thirdly, the phone only booted after I reset it by holding down the power and home buttons simultaneously.
It seems to me that although the phone was completely unresponsive and seemed to have switched itself off, it was actually still on and it was only the display that had stopped working.
The 6S was on 9.0.1 when it happened.
However, whereas the 6 would restart again as soon as I pressed the power button, the incident with the 6S this week was different.
Firstly, it wouldn't power back up again when I pressed the power button.
Secondly, my Apple Watch didn't show that it had lost contact with the phone, and the watch apps continued to function normally, which they cannot do unless the phone is on.
Thirdly, the phone only booted after I reset it by holding down the power and home buttons simultaneously.
It seems to me that although the phone was completely unresponsive and seemed to have switched itself off, it was actually still on and it was only the display that had stopped working.
The 6S was on 9.0.1 when it happened.