A security issue

This semester, I am teaching in a traditional classroom where I used to use an overhead projector to display my teaching materials to the class. This is where I decided to start my iPad classroom experience. When I was practicing the presentation in my office with a projector, I found that presentations of class materials from the iPad can be very dynamic, real-time zoom makes the presentations clear to the students, and switching between pages on the iPad is quick and easy.  

When I was teaching with the iPad for the very first time, I was presenting the class materials with all these excellent features of the iPad to the class. Everything worked well until there was a page where I had to stay there for more than five minutes for detailed explanation. The iPad automatically turned off after this 5 minutes because of the unchangeable security setting. I had to turn the iPad on again to show the class materials. When I entered the passcode on the iPad, the number actually lit up and the whole class was watching me entering the passcode on the iPad. I ended up changing my code after the class.

This was where I found the security flaw when using our iPad to display the class materials.  Do you have this problem? How do you solve it?