the live tracking idea is great and i'm sure represents the way forward for fell running, not just in terms of safety but also for interest of non-participants. imagine being able to follow the progress of championship races on the net as they happen, although some of those with sneaky lines might not be so pleased.
in terms of the auto-response to a static tracker this may well be an issue at present. the technology isnt 100% robust, in the recent spine race there were instances of competitors appearing to have stopped only to find that it was a signal dead spot. however it is important that we use this hardware now as it will encourage future development and ultimately bring the costs down.
how about using mobile phones as an intermediate response. if competitors were asked, (not necessarily mandated), to carry a mobile the first repsonse to a static transponder would be to call that competitors mobile. if they didnt have one, or there was no response you could call the competitor who was next due to arrive at the spot and ask them to investigate.
this would also reinforce the ethos that competitors form part of the overall saftey package, another fell running tradition.