Hmm... perhaps I didn't think everything out. I think the radio protocol is still a problem, but yeah, if no one can use the frequency, why would they monitor it?

Nomad, is your solution the same as something proposed like 2 or more years ago? The proposal was using an attention CTCSS tone for a duration of like a few seconds. I think that has merit, but still seems too complicated for an emergency.

The military uses key-clicks sometimes to pass messages. What about keyclicks in the format of SOS? I would think someone might be able to create an add-on for a radio that plugs into the headset jack. Then you could passively monitor. No fiddling with CTCSS tone, compatible with older radios, and possibly a modification of existing technology. I've seen the CW receivers that will display CW on an LCD screen. Can those be used with human operators on the other end? If so, maybe there is already pattern recognition technology that could "understand" an SOS made out of key breaks.