How a mobile service provider knows wether a mobile is switched off or out of range?

Question

I was having doubt how a mobile service provider knows that mobile is switched off. wether the mobile sends some special signal before going to off mode? can u suggest me some good links to have details of this.

Answer 1

when the phone is turned off it de-registers from the Tower, (kinda like turning the light off) the tower registers all the phone #'s that are connecting/bouncing off to get the signal.

if you are out of range then the tower does not register your phone# at all, if you loose the signal it is registered as last place it was on and getting the signal