Will Apple know that I opened my phone?

Hey guys, I've got a question concerning the changing of the iphone backpanel.

I'm asking myself if there is any seal that gets broken when I change the backpanel of the phone.

I'm asking you, because I think this could be interessting to everyone who wants to change the back.

In case that you just want to get your phone a new look etc. , maybe with a different-colored back, it would be nice to know whether you lose your apple warrenty, or not.

Thank you for your time ;)

greetz, M.Tenz