In previous generations of iPhones, there was a way to force-reboot an iPhone when something really strange happened. We press the power button together with home button for a few seconds until the screen flashes and Apple logo is displayed on top of white background. Not that it was needed a lot, I can recall less than 5 times I needed to use it since my first ever iPhone 3G, that was 9 years ago.
So, I installed an app out of curiosity, and ever since I tried to open it, my iPhone 7 had been behaving strangely. I tried using the force-reboot using the way I used to do it, but this time it didn’t work. I got confused for a few minutes until I realised that starting from iPhone 7, the home button is no longer a physical button. This force-reboot needs to use 2 physical buttons, so I tried the other combinations. With the removal of physical home button, there are only 3 physical buttons remaining: power, volume up and volume down. I suspected that power button will remain part of the combo, so I first tried pressing power button and volume up simultaneously for a few seconds. Nothing happened other than my volume was set to maximum.
There it is: to force-reboot an iPhone 7, what we need to do is pressing power button and volume down button together for a few minutes until the Apple logo on a white background appears. You would need to enter your PIN again after force-reboot before you can use Touch ID again.
Quick and simple. I hope this helps.