Designed to boot the screen saver without any operation for a certain period of time

I am developing an iPad app using swift on iOS.

What you want to do is
"Start the screen saver without any operation for a certain period of time"
However, how do you design
Detect No Operations for a certain period of time? I'm worried about whether it will come true.

It's a screen saver, so if you don't operate any screen for a certain period of time, you have to start it.Therefore, we have to get information that the operation has been done on any screen, but it is not realistic to include the process of checking the operation on all screens, so we are wondering if there is a good way.

Could you give me some advice on what kind of design is good?
Thank you in advance.