What a neat school project. I know it has been a week since your posting, but thought I would respond anyway just in case you are still working on your project.
I would definitely purchase a hair straightener or hot rollers that automatically turned themselves off. As the parent of a teenager, I would gladly pay more for a product with this feature so that I could have the reassurance that the product is off and all is safe.
Best of luck on your project and keep up that entrepreneurial spirit!