sos only on a mobile phone.

[stanwixman]

The answer is probably glaringly obvious and starring me in the face but can anyone put me out of my misery. I was lying awake in bed in the early hours and stupid daft thoughts kept wafting in and out of my head as they do. One in particular is when a mobile phone has no signal it swiches to emergency calls only. If this is the case how do they get a signal when the phone operators cant. Is there a diferent frequency or diferent means of comunicating to the phone or something?

[pug100]

If your mobile has no signal then it can't do anything, either send or receive. Some phones have an option to send text only when the battery is low, but you'll still need to be within ranfe of a phone mast to send it.
This site explins it well
http://electronics.howstuffworks.com/cell-phon e.htm

More in depth here

http://en.wikipedia.org/wiki/Cell_phone

BTW the Americans correctly use the term cell phone rather than mobile phone.

[rojash]

When your phone says it has no signal, it will normally mean no signal to your own service provider. SOS calls use "roaming" technology and will automatically be routed via any other available service provider.

BTW, I wonder why Pug100 thinks the term "cell phone" is more correct than "mobile phone"? The former describes the technology, while the latter describes the functionality. To most people, the functionality is the important part!