As mentioned above you do not have to respond if you dont want to/are not available.
We have a similar system with the Wales Emergency Response Team.
(I have to point out at this point that Powys 4x4 response has had such a big impact in Wales that it has now been rolled out across Wales and we are looking for new members in the North, South and West of Wales. Bear in mind that you dont even have to live in Wales to become a member, even if you live on the borders somewhere in England you may be able to get into an area of Wales that it would take a Welsh member sometime to get to, especially if they have to go across country.)
Basically you get a txt asking you if you are able to go on standby, then you log onto the emergency website and say what hours you are available. If you are unable to log on you send a reply txt stating available hrs or unavailable hrs. After that you may or may not get a call.
Usually the person closest/most suitable to the job will be called first, then it goes down in decreasing order until someone responds.
For example, I dont have a snorkel so may not get called out in a situation where there has been flooding, but I may get called out if there is plenty of snow or ice. Really it depends on who has the closest/most suitably equipped vehicle.
Lawrence. Radnor is a great place to play. When the Wales response group have it they rent it for the weekend which gives us exclusive access to the whole area. We do still have to look out for walkers/cyclists etc but it means we can explore (play) plenty of places you generally arent allowed to go as a generic member of the public.
I also drink Port and I'm not ashamed to say it!
Me Truck