This has been mentioned before by G6WRW but there was little response so I thought I would mention it again as it’s technically interesting. I refer to the EmergencySMS service.
Full details can be found at http://www.emergencysms.org.uk so there is no need to say more about how it’s used here, just go to their site.
How it works however is interesting, it allows a text to be sent (by a registered phone only) to the emergency services even if your phone is showing no network.
I believe it uses one of the control channels to communicate with a tower and it is independent of the network operator. The control channels communicate with the tower and that is how they decide if the signal strength is sufficient to allow a voice connection, else a “no network” message shows on your phone.
Registration is free and very simple, just go to the url above.
I am sure there’s someone out there who could provide a much better (more accurate) explanation of what actually goes on?
Anyway, I have been using the system for 4 years and like my PLB I hope I never have to use it.
All the best
George M0HAJ
If your phone shows “no network” then you will not send anything for there is no network to carry the call.
What will work is when your phone can hear other networks but not your own, in this case emergency calls can be made. Likewise, you can make emergency calls without a SIM. In both these cases your phone shows something like “emergency calls only”.
This service allows you to send text messages to the 999 service and by registering the phone, the emergency networks know more about you so you don’t have to send as much in the text.
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Correct!