How will cell phone companies/providers know you opened a device?

Question

Warrenty states thast if you open a device in any way your warranty will be voided.

Im very curious. If you were to open your phone and put it back together perfectly, how would they even know you opened it in the first place?

Example: Removing a plastic screen off a pda phone and then putting it back.

Removing screws etc.

Oh and little off topic but um how does the "refurbished" phones process work? How can some be used.. yet look brand new?

Answer 1

There is only certain parts that they don't want you to mess with. Usually, they put some sort of sticker over it, and they can tell if you have removed that piece.

and...idk....