Mobile phones

[Allen Crisp]

If I call someone who is on a landline then the position of the receiving phone is fixed, as there is a wire going into the building, so the signal knows where to go, if you see what I mean. If I call someone who is on a mobile they could be anywhere, so I assume that the signal has to go everywhere to make sure it reaches them. They could even be abroad! Does this mean that a signal from every mobile call presently taking place is inside my empty teacup?

[WoWo]

No, what happens is that as you move around it registers with a base station when the phone goes out of range of the base station it is picked up by the next and so on. When you phone a mobile the system knows which base station it last contacted with and uses that.

[rojash]

This is how it's possible to locate someone's whereabouts by means of their mobile. All the time your mobile is switched on it is effectively shouting "Here I am", so that the network knows which cell it's in.

[theprof]

WoWo and rojash are both right on this one.

I'd like to add that some recent mobiles periodically contact the appropriate base station within the cell twenty-four hours a day at least once in every hour to report in.

You are not made aware of this transmission and this is one of the reasons why modern mobiles seem to need recharging more often than older mobiles.